JP3786973B2 - Electrode, method for producing the electrode, and battery using the electrode - Google Patents

Electrode, method for producing the electrode, and battery using the electrode Download PDF

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JP3786973B2
JP3786973B2 JP51764999A JP51764999A JP3786973B2 JP 3786973 B2 JP3786973 B2 JP 3786973B2 JP 51764999 A JP51764999 A JP 51764999A JP 51764999 A JP51764999 A JP 51764999A JP 3786973 B2 JP3786973 B2 JP 3786973B2
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electrode
conductive material
battery
positive electrode
electronic conductive
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万希子 吉瀬
省二 吉岡
淳 荒金
広明 漆畑
久 塩田
英夫 堀邊
茂 相原
大吾 竹村
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Mitsubishi Electric Corp
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Description

技術分野
この発明は、電極、この電極の製造方法、およびこの電極を用いた電池に関するものであり、詳しくは温度の上昇に伴い、その抵抗が大きくなる電極、この電極の製造方法および、この電極を用いた電池に関するものである。
背景技術
近年、電子機器の発達にともない電源として使用されている電池の高容量化および高出力密度化が進みつつある。これらの要求を満たす電池として、リチウムイオン二次電池が注目されている。このリチウムイオン二次電池はエネルギー密度が高いという利点の反面、非水電解液を使用することなどから安全性に対する十分な対応策が必要とされる。
従来、安全に対する対応策として、安全弁により内部圧力の上昇を逃がす、あるいは外部短絡による発熱に応じて抵抗が上昇して電流を遮断するＰＴＣ素子を電池に組み込むなどが提案されていた。
たとえば、特開平４−３２８２７８号公報に開示されているように、円筒型電池の正極キャップ部分に安全弁とＰＴＣ素子を装着する方法が知られている。しかし、安全弁が動作すると、大気中の水分が電池内部に侵入し、リチウムが負極に存在すると発熱反応が起こる恐れがある。
一方、ＰＴＣ素子は外部短絡回路を遮断し、動作による弊害もない。このＰＴＣ素子は例えば、外部短絡によって電池が９０（度）以上の温度になると動作するように設計することによって、電池異常時にまず最初に動作する***品とすることができる。
従来のリチウム二次電池は上述のような構成を有しているため、以下に示すような問題を有している。
従来のリチウム二次電池はリチウム二次電池内部に短絡が発生し温度が上昇したとき、この短絡電流の増加を抑制できないことである。
リチウム二次電池内部における短絡が発生し温度が上昇した時に、正極と負極の間に配置した、ポリエチレンやポリプロピレン製のセパレータが軟化または溶融することにより、セパレータの孔部が閉塞され、これによってセパレータに含有された非水電解液を押し出したり、封じ込めたりしてセパレータ部分のイオン電導性が低下し、短絡電流が減衰する機能がセパレータに期待されている。
しかし、発熱部分から離れたところのセパレータは必ずしも溶融するとは限らない。また、さらに温度が上昇した場合にはセパレータが溶融、流動することにより、正負極を電気的に絶縁する機能が失われ、短絡につながることも考えられる。
また、特にリチウムイオン二次電池の場合、負極は集電体となる銅箔などの基材上に黒鉛などの負極活物質と、ＰＶＤＦ（ポリフッ化ビニリデン）などのバインダーと、溶剤とを含むスラリーを塗布し、乾燥して薄膜を形成している。正極も同様に集電体となるアルミ箔などの基材上に薄膜として形成される。
ただし、正極はＬｉＣｏＯ2などの正極活物質とバインダーと導電助剤とを含むものである。
導電助剤とは正極活物質の電子導電性が悪いとき、正極の電子導電性をより高くするためのものである。導電助剤は例えばカーボンブラック（例えばアセチレンブラック）、黒鉛（例えばＫＳ−６）などである。
このような電池は内部短絡などで電池温度がセパレータが溶融、流動するような温度以上に上昇したとき、セパレータが流動した部分では正極と負極との間に大きな短絡電流が発生するため、発熱により電池の温度が更に上昇し、短絡電流が更に増大するといった問題がある。
この発明は上述の問題を解決するためになされたものであり、温度の上昇に伴い抵抗が上昇する電極、この電極の製造方法、この電極を用いた電池を得ることを目的とするものである。
発明の開示
この発明に係る第１の電極は、活物質と、
この活物質に接触する電子導電性材料とを有する電極であって、
上記電子導電性材料は、導電性充填材と樹脂とを含有し、温度が上昇するとともに、その抵抗が増加するように構成し、上記電子導電性材料の粒径は０．０５（μｍ）〜１００（μｍ）としたことを特徴とするものである。
これによれば、上記電子導電性材料は、導電性充填材と樹脂とを含有し、温度が上昇するとともに、その抵抗が増加するように構成したので、温度が上昇したとき、電極に流れる電流の増大を抑制することができる。また、電子導電性材料の粒径を０．０５（μｍ）〜１００（μｍ）としたので、電極の抵抗の変化率が増大する現象が生じる前の電極の抵抗を低くし、かつこの電極を電池に適用したときの放電容量を大きくすることができる。
この発明に係る第２の電極は、電子導電性材料の樹脂は９０（度）〜１６０（度）の範囲内で融点を有するものを用いたことを特徴とするものである。
これによれば、電子導電性材料の樹脂は９０（度）〜１６０（度）の範囲内で融点を有するものを用いたので、電子導電性材料は９０（度）〜１６０（度）の範囲内の所定の温度付近で抵抗が増大する。
この発明に係る第３の電極は、電子導電性材料を活物質層の全固形分１００重量部に対し０．５〜１５重量部含有したものである。
これによれば、電子導電性材料を０．５〜１５重量部含有したものを用いたので、電極の抵抗の変化率が増大する現象が生じる前の電極の抵抗を低くすることができる。
この発明に係る第４の電極は、電子導電性材料の導電性充填材の割合が４０重量部〜７０重量部としたことを特徴とするものである。
これによれば、電子導電性材料の導電性充填材の割合が４０重量部〜７０重量部としたので、所定の温度付近での電極の抵抗の変化率が大きく、かつこの電極を電池に適用したときの電池の放電容量を大きくすることができる。
この発明に係る第５の電極は、導電性充填材はカーボン材料または導電性非酸化物としたことを特徴とするものである。
これによれば、導電性充填材はカーボンまたは導電性非酸化物としたので、電極の導電性を高めることができる。
この発明に係る第６の電極は、電極は電子導電性を高めるものであって、温度の上昇に伴いその抵抗がほとんど変化しない導電助剤を含むことを特徴とするものである。
これによれば、第６の電極は電子導電性を高めるものであって、温度の上昇に伴いその抵抗がほとんど変化しない導電助剤を含むので、電子導電性材料の電子導電性が低いものを用いても電極の抵抗を適切なものに調節することができる。
この発明に係る第７の電極は、少なくとも種類の異なる２つの電子導電性材料を含有することを特徴とするものである。
これによれば、少なくとも種類の異なる２つの電子導電性材料を含有するので、所定の温度よりも低い温度での抵抗が低く、柔軟性の高い電極が得られるとともに、この電極を用いて電池を構成したとき、電池の内部の温度が所定の温度以上に上がったとき電極の抵抗が大きくなり、電池内部に流れる電流が減少するので電池の安全性が向上する。
この発明に係る第８の電極は、電子導電性材料は少なくとも種類の異なる２つの導電性充填材を含有することを特徴とするものである。
これによれば、電子導電性材料は少なくとも種類の異なる２つの導電性充填材を含有するので、所定の温度よりも低い温度での抵抗が低く、柔軟性の高い電極が得られるとともに、この電極を用いて電池を構成したとき、電池の内部の温度が所定の温度以上に上がると、電極の抵抗が大きくなり、電池内部に流れる電流が減少するので電池の安全性が向上する。
この発明に係る第９の電極は、電子導電性材料は少なくとも種類の異なる２つの樹脂を含有することを特徴とするものである。
これによれば、電子導電性材料は少なくとも種類の異なる２つの樹脂を含有するので、所定の温度よりも低い温度での抵抗が低い電極が得られるとともに、この電極を用いて電池を構成したとき、電池の内部の温度が所定の温度以上に上がったとき電極の抵抗が大きくなり、電池内部に流れる電流が減少するので電池の安全性が向上する。
この発明に係る第１の電池は、正極と、負極と、上記正極および上記負極の間セパレータを備え、
上記正極または上記負極に第１電極から第９の電極のいずれかを用いたことを特徴とするものである。
これによれば、上記正極または上記負極に第１の電極から第９の電極のいずれかを用いたので、電池の内部の温度が所定の温度以上に上がったとき電極の抵抗が大きくなり、電池内部に流れる電流が減少するので、電池の安全性が向上する。
この発明に係る第１の電極の製造方法は、
（ａ） 導電性充填材と樹脂とを含有する電子導電性材料を粉砕する工程
（ｂ） 粉砕した電子導電性材料と活物質とを分散させることにより活物質ペーストを製造する工程
（ｃ） 上記活物質ペーストを乾燥させたものを所定の温度、所定の圧力でプレスする工程
なる工程を有することを特徴とする。
これによれば、（ａ）〜（ｃ）の工程を有するので、電子導電性材料同士のつながりが良くなるので、所定の温度よりも低い温度での電極の抵抗を低くすることができる。
この発明に係る第２の電極の製造方法は、第１の電極の製造方法において、所定の温度を樹脂の融点または融点付近の温度としたことを特徴とする。
これによれば、所定の温度を樹脂の融点または融点付近の温度としたので、電子導電性材料同士のつながりが更に良くなり、所定の温度よりも低い温度での電極の抵抗を更に低くすることができる。
この発明に係る第３の電極の製造方法は、第１の電極の製造方法において、導電性充填材と樹脂とを含有する電子導電性材料を粉砕する工程は、超音速流にのせた上記電子導電性材料を壁面にあてるかまたは上記電子導電性材料を互いに衝突させることにより、上記電子導電性材料を粉砕することを特徴とする。
これによれば、超音速流にのせた上記電子導電性材料を壁面にあてるかまたは上記電子導電性材料を互いに衝突させることにより、上記電子導電性材料を粉砕するため、粒径が小さい電子導電性材料を得ることができ、この電子導電性材料を用いて電極を製造すると、所定の温度よりも低い温度での電極の抵抗を更に低くすることができる。
この発明に係る第４の電極の製造方法は、第１の電極の製造方法において、導電性充填材と樹脂とを含有する電子導電性材料を粉砕する工程は、上記電子導電性材料に剪断力、磨砕力および衝撃力を複合的に与えることにより上記電子導電性材料を粉砕することを特徴とする。
これによれば、上記電子導電性材料に剪断力、磨砕力および衝撃力を複合的に与えることにより上記電子導電性材料を粉砕するので、粒径のばらつきが少ない電子導電性材料を得ることができ、この電子導電性材料を用いて電極を製造すると、柔軟性が高い電極を得ることができるため、電極の加工が容易になる。
この発明に係る第５の電極の製造方法は、第４の電極の製造方法において、電子導電性材料を冷却しながら粉砕することを特徴とする。
これによれば、電子導電性材料を冷却しながら粉砕するので、粒径のばらつきが更に少ない電子導電性材料を得ることができ、この電子導電性材料を用いて電極を製造すると、柔軟性が更に高い電極を得ることができるため、電極の加工が更に容易になる。
【図面の簡単な説明】
第１図は電池の構成を説明するための図、第２図は電極の体積固有抵抗、抵抗変化率、電池の放電容量を示す表図、第３図は釘刺し試験を行ったとき経過時間と電池の温度との関係を示すグラフ図、第４図は釘刺し試験を行ったとき経過時間と電池の温度との関係を示すグラフ図、第５図は電極の体積固有抵抗、温度上昇時の抵抗変化率、電池の放電容量、および釘刺し試験開始１０分後の電池の温度を示す表図、第６図は電子導電性材料の割合と電極の抵抗値との関係および電子導電性材料の割合と放電容量との関係を示すグラフ図、第７図は電子導電性材料の粒径と電極の体積固有抵抗との関係及び電子導電性材料の粒径と放電容量との関係を示すグラフ図、第８図は電子導電性材料の平均粒径、電極の抵抗、及び電池の放電容量を示す表図、第９図は電極の気孔率、体積固有抵抗、放電容量を示す表図、第１０図は電極の体積固有抵抗、電池の放電容量、釘刺し試験開始１０分後の電池の温度を示す表図、第１１図は電極に用いる電子導電性材料の平均粒径を示す表図、第１２図は複合粉砕方式により粉砕する前の電子導電性材料の粒径、複合粉砕方式により粉砕した後の電子導電性材料の粒径を示す表図、第１３図は電極の体積固有抵抗値、電極の柔軟性、電池の短絡電流値を示す表図、第１４図は電極の体積固有抵抗値、電極の柔軟性、電池の短絡電流値を示す表図、第１５図は電極の体積固有抵抗値、電極の柔軟性、短絡電流値を示す表図、第１６図は電池の短絡電流値を示す表図、第１７図は電池の短絡電流値を示す表図、第１８図は円筒型の電池の一例を示した図である。
発明を実施するための最良の形態
第１図は本発明の電池を説明するための図であり、詳しくは電池の縦断面図である。
図において、１は正極、２は負極、３は正極１と負極２との間に設けられたセパレータである。
正極１は正極集電体４と正極活物質層６とを有する。
負極２は負極集電体５と負極活物質層７とを有する。
正極１は正極集電体４となる金属膜（例えばアルミニウムなどの金属膜）の表面に正極活物質層６を形成したものである。
負極２は負極集電体５となる金属膜（例えば銅などの金属膜）の上に、カーボン粒子などの負極活物質をバインダで成形した負極活物質層７を形成したものである。
セパレータ３は例えばリチウムイオンを含有する電解液を保持したものである。
正極活物質層６は正極活物質８と電子導電性材料９とバインダ１０とを有する。
正極活物質８は例えば、コバルト系酸化物、マンガン系酸化物、鉄系酸化物等である。
コバルト系酸化物とは、例えばＬｉＣｏＯ2結晶、またはＬｉＣｏＯ2結晶において、一部のＣｏ原子が遷移金属原子（例えばＮｉ原子、Ｍｎ原子など）に置き換えられたものである。
マンガン系酸化物とは、例えばＬｉＭｎＯ2、ＬｉＭｎ2Ｏ4、ＬｉＭｙＭｎ2−ｙＯ4（Ｍ：Ｃｒ、Ｃｏ、Ｎｉなど）である。
鉄系酸化物とは、例えば、ＬｉＦｅＯ2、Ｌｉ5ＦｅＯ4、Ｆｅ2（ＳＯ4）3である。
正極活物質８と電子導電性材料９とはバインダ１０により結合しているので、これらの一部は互いに接触している。
正極活物質８は粒子状のものであり、電子導電性材料９は正極活物質８よりも小さな形状を有する粒子状のものである。
電子導電性材料９は例えば導電性充填材と樹脂とを含有するものである。
電子導電性材料９は温度の上昇とともにその抵抗が上昇する特性を有するものであり、特に温度が９０（度）〜１６０（度）範囲内の所定の温度付近で、その抵抗値の変化率が大きくなり、これによりその抵抗が上昇するＰＴＣ特性を有するものである（以後この特性をＰＴＣ（Ｐｏｓｉｔｉｖｅ Ｔｅｍｐｅｒａｔｕｒｅ Ｃｏｅｆｆｉｃｉｅｎｔ）と称す）。
導電性充填材とは、例えばカーボン材料、導電性非酸化物といったものである。
カーボン材料とは、例えばカーボンブラック、グラファイト、カーボンファイバー等である。
カーボンブラックとは、例えばアセチレンブラック、ファーネスブラック、ランプブラック、サーマルブラック、チャンネルブラック等である。
導電性非酸化物とは、例えば金属炭化物、金属窒化物、金属ケイ素化物、金属ホウ化物といったものである。
金属炭化物とは例えば、ＴｉＣ、ＺｒＣ、ＶＣ、ＮｂＣ、ＴａＣ、Ｍｏ2Ｃ、ＷＣ、Ｂ4Ｃ、Ｃｒ3Ｃ2等である。
金属窒化物とは、例えばＴｉＮ、ＺｒＮ、ＶＮ、ＮｂＮ、ＴａＮ、Ｃｒ2Ｎ等である。
金属ホウ化物とは、例えばＴｉＢ2、ＺｒＢ2、ＮｂＢ2、ＴａＢ2、ＣｒＢ、ＭｏＢ、ＷＢ等である。
また、樹脂とは、例えば高密度ポリエチレン（融点：１３０（度）〜１４０（度））、低密度ポリエチレン（融点：１１０（度）〜１１２（度））、ポリウレタンエラストマー（融点：１４０（度）〜１６０（度））、ポリ塩化ビニル（融点：約１４５（度））等の重合体であり、これらはその融点が９０（度）〜１６０（度）の範囲にある。
電子導電性材料９において、ＰＴＣの機能が発現する温度は電子導電性材料９に含まれる樹脂の融点に依存するため、樹脂の材質または種類を変えることにより、ＰＴＣの機能が発現する温度を９０（度）〜１６０（度）の間の温度に調節することが可能である。
また、電子導電性材料９に含まれる樹脂を結晶性樹脂とすれば、電子導電性材料９のＰＴＣの機能が発現する温度付近での抵抗変化率を更に大きくすることができる。
このＰＴＣ特性は、２回以上複数回発現できるような可逆性のあるものでもよいし、一度ＰＴＣの機能が発現した後に温度を下げたときに、もとの抵抗値にもどらないような可逆性が無いものでも良い。
このＰＴＣの機能が発現する温度が９０（度）以下であることは安全性の確保という観点からは好ましいが、電池が通常使用される温度範囲において電極の抵抗値が上昇することになるので、負荷率特性などにおいて電池の性能低下が起こる。
また、このＰＴＣの機能が発現する温度が１６０（度）を越す場合には、電池の内部温度がこの温度まで上昇することになり、安全面の観点から好ましくない。
従って、電子導電性材料９において、ＰＴＣの機能が発現する温度は９０（度）から１６０（度）の範囲にあるように設計することが望ましい。
ＰＴＣの機能が発現する温度は樹脂の融点に依存するため、樹脂はその融点が９０（度）から１６０（度）の範囲にあるものを選択している。
また、電子導電性材料９において、正常時（つまり、ＰＴＣの機能が発現する前）における電極の抵抗の大きさは、正極活物質層６全体に対する電子導電性材料９の割合を変えることにより調節することができる。
この電子導電性材料９は、その中に含まれる樹脂が軟化、溶融し、体積膨張することにより、電子導電性材料９自身の抵抗値が上昇するため、ＰＴＣの機能が発現する。
本発明の電池の正極１は、正極活物質層６に含まれる電子導電性材料９自身がＰＴＣ特性を有するので、正極１の温度が電子導電性材料９において、ＰＴＣの機能が発現する温度よりも大きくなると、正極活物質層６の抵抗値が増大する。
従って、このような特性を有する電極（ここでは電池の正極１に適用）を電池に適用したとき、電池の外部または内部における短絡により電流が増大し、電池もしくは電極の温度がある程度以上に上昇した場合において正極活物質層６自体の抵抗値が高くなるので、電池内部に流れる電流が抑制される。
従って、この電極を用いて電池を構成したとき、電池の安全性は飛躍的に向上し、厳しい条件上での短絡、逆充電あるいは過充電等の異常時においても電池の安全性が保たれるという効果を奏する。
ここでは、正極活物質層６は正極活物質８と電子導電性材料９とバインダ１０とを有するものを例に説明したがこれに限定されるものではない。
例えば、正極活物質層６に含まれる正極活物質６の電子導電性が低いような材質を用いている場合、正極活物質層６に更に導電助剤を加えることにより、これを補うことが可能となる。
また、電子導電性材料９は粒子状としたが、その形状はファイバー状、鱗片状の小片であっても良い。要は、隣り合う正極活物質８の間に電子導電性材料９が位置することができるような大きさを有するものであればその形状はどのようなものであっても良い。
ここでは正極１、特に正極活物質層６に導電性充填材と樹脂とを含む電子導電性材料の構成を開示したが、これに限定される必要はなく、負極２に上述の構成を適用し、これを用いて電池を構成しても同様の効果を奏する。
次に、正極１の製造方法、負極２の製造方法の一例、正極１と負極２を用いた電池の製造方法の一例を説明する。
（正極の製造方法）
室温における体積固有抵抗が十分低く、９０（度）〜１６０（度）の間の所定の温度よりも大きい温度での体積固有抵抗が大きな電子導電性材料（例えば導電性充填材と樹脂とを所定の割合で含むペレット）を細かく粉砕し、電子導電性材料の微粒子を得る。
電子導電性材料を粉砕する方法として、圧縮した空気または圧縮した窒素またはアルゴン等の不活性ガスを使用して粉砕する方法がある。
この方法を具体的に実現する手段として、上述したものにより超音速の気流を発生させ、この気流中において、電子導電性材料の粉体を互いに衝突させるか、もしくはこの気流中にある粉体を壁面（図示せず）に衝突させることにより、電子導電性材料を粉砕し、粒径の小さい電子導電性材料の微粒子を得ることができる（これにより電子導電性材料の微粒子を得る方式をジェットミル方式と称す）。
特に、得られる電子導電性材料の粒径を小さくするには、ジェットミル方式により電子導電性材料を粉砕するのが望ましい。
また、電子導電性材料を粉砕する他の方法として、電子導電性材料に剪断力、磨砕力および衝撃力を複合的に与えることにより、粉砕する方法がある。
この方法を具体的的に実現する手段として、例えば、高速回転するローター（図示せず）とステーター（図示せず）との凹凸の刃により、電子導電性材料を粉砕することにより、電子導電性材料の微粒子を得ることができる（これにより電子導電性材料の微粒子を得る方式を複合粉砕方式と称する）。
また、電子導電性材料を粉砕する他の方法として、電子導電性材料をボールミルに入れて回転して電子導電性材料を剪断することにより、粉砕する方法がある（これにより電子導電性材料の微粒子を得る方式をボールミル方式と称す）。
特に、複合粉砕方式またはボールミル方式により電子導電性材料を粉砕した後、ジェットミル方式により粉砕すれば、得られる電子導電性材料の微粒子の粒径、および粒径のばらつきを小さくすることができる。
更に、電子導電性材料を冷却しながら粉砕すれば、得られる電子導電性材料の粒径を小さくすることができる。
次に、この電子導電性材料の微粒子、正極活物質（例えばＬｉＣｏＯ2）、バインダー（例えば、ＰＶＤＦ）を分散媒（例えばＮ−メチルピロリドン（以下、ＮＭＰと略す））に分散させることにより調整し、正極活物質ペーストを得た。
次に、上述の正極活物質ペーストを、正極集電体４となる集電体基材（例えば所定の厚さを有する金属膜）上に塗布した。
さらに、これを乾燥させた後、所定の温度でかつ所定の面圧でプレスし、所望する厚さを有する正極活物質層６を形成し、正極１を得た。
ここで示した電極（詳しくは正極１）の製造方法では、所定の温度、所定の面圧でプレスしているため、正極集電体４と正極活物質層６との密着性が良くなり、正極集電体４と正極活物質層６との間の接触抵抗が低くなる。
更に、電子導電性材料９同士のつながりが良くなるので、集電ネットワークが多く形成され、正常時の正極活物質層６の抵抗を低くすることができる。
これにより、正常時における電極の抵抗を低くすることができる。
つまり、電極をプレスするときの温度、圧力（ここでは面圧）を調節することにより、製造される電極の抵抗を調節することができる。
特に、所定の温度を電子導電性材料９に含まれる樹脂の融点または融点付近の温度にすると、正極集電体４と正極活物質層６との密着性が更に良くなるので、正極集電体４と正極活物質層６との間の接触抵抗を更に低くすることができる。
更に、電子導電性材料９が変形し、正極活物質の間に入りこむとともに、電子導電性材料９同士のつながりが更に良くなるので、集電ネットワークがより多く形成され、正常時における電極の抵抗を更に低くすることができる。
ここでは、乾燥させた正極活物質ペーストを所定の温度でかつ所定の面圧でプレスする例を説明したが、乾燥させた正極活物質ペーストを所定の面圧でプレスした後、この正極活物質ペーストを所定の温度（望ましくは融点または融点付近の温度）で加熱することにより、正極１を得るにようにしてもよい。
次に、本発明の電池の負極２の製造方法について説明する。
（負極の製造方法）
メソフェーズカーボンマイクロビーズ（以下、ＭＣＭＢと略す）、ＰＶＤＦをＮＭＰに分散して作製した負極活物質ペーストを、負極集電体となる集電体基材（例えば所定の厚さを有する金属膜）上に塗布し、乾燥させた後、所定の温度、所定の圧力でプレスし、負極活物質層７を形成した負極２を得ることができる。
次に本発明の電池の製造方法について説明する。
（電池の製造方法）
上述の方法により得られた正極と負極との間にセパレータ（例えば多孔性のポリプロピレンシート）を挟み両極を貼りあわせた後、電解液を注液し、正極、負極を有する一対の電池を得た。
上述の方法により得られる電池は、正極が温度の上昇に伴い抵抗が上昇する特性を有するものであるため、電池の外部または内部で短絡事故が発生し、電池の温度が上昇しても、短絡電流の上昇を抑制するため、電池自身の安全性が向上する。
実施例１．
（正極の製造方法）
室温における体積固有抵抗が０．２（Ω・ｃｍ）、１３５（度）における体積固有抵抗が２０（Ω・ｃｍ）の特性を有する電子導電性材料（例えばカーボンブラックを６０重量部、ポリエチレンを４０重量部の割合で含むペレット）をジェットミル方式により細かく粉砕し、電子導電性材料の微粒子を得た。
次に、この微粒子を６重量部、正極活物質（例えばＬｉＣｏＯ2）を９１重量部、バインダー（例えばＰＶＤＦ）を３重量部を分散媒であるＮＭＰに分散させることにより調整し、正極活物質ペーストを得た。
次に、上述の正極活物質ペーストを、正極集電体４となる厚さ２０（μｍ）の金属膜（ここではアルミニウム箔）上にドクターブレード法にて塗布した。
更に、８０（度）で乾燥した後、所定の温度（例えば室温）でかつ所定の面圧（例えば２（ｔｏｎ／ｃｍ2））でプレスし、正極集電体４の上に厚さ約１００（μｍ）の正極活物質層６を形成した正極１を得た。
（負極の製造方法）
メソフェーズカーボンマイクロビーズ（以下、ＭＣＭＢと略す）９０重量部、ＰＶＤＦ１０重量部をＮＭＰに分散して作製した負極活物質ペーストを、厚さ２０（μｍ）の銅箔からなる負極集電体上に、ドクターブレード法にて塗布し、８０（度）で乾燥させた後、室温で、２．０（ｔｏｎ／ｃｍ2）圧力でプレスし、負極集電体５の上に負極活物質層７を形成した負極２を得た。
（電極及び電池の評価）
本発明の電極、この電極を用いた電池の評価を行うため以下に示すような方法を用いて評価を行った。
（電極の抵抗測定）
電極の両面にアルミニウム箔を融着し、一方のアルミニウム箔の片面にプラス側の電圧端子、電流端子を、もう一方のアルミニウム箔にマイナス側を接続した。端子にはヒーターが接しており、５（度／分）の昇温速度で電極を昇温しながら、定電流を流した素子の電圧降下を測定することにより抵抗値（ここでは体積固有抵抗（Ω・ｃｍ））を求めた。
（容量試験）
上述の方法により得られる正極１、負極２をともに１４（ｍｍ）×１４（ｍｍ）の大きさに切断した。
次に多孔性のポリプロピレンシート（ヘキスト製商品名セルガード＃２４００）をセパレータ３とし、これを正極１と負極２との間にはさみ両極を貼りあわせたものを単電池とした。
単電池の正極集電体４、負極集電体５をそれぞれスポット溶接することにて取り付け、これをアルミラミネートシートより作製した袋に入れて、エチレンカーボネートとジエチルカーボネートの混合溶媒（モル比で１：１）に６フッ化リン酸リチウムを１．０（ｍｏｌ／ｄｍ3）の濃度で溶解した電解液を注液した後、熱融着で封口し電池とした。
この電池の室温での充放電試験を実施し、２Ｃ（Ｃ：時間率）における放電容量を測定した。
（釘刺し試験）
上述の方法により得られる正極１、負極２をともに５０（ｍｍ）×５０（ｍｍ）に切断した。
次に多孔性のポリプロピレンシート（ヘキスト製商品名セルガード＃２４００）をセパレータ３とし、これを正極１と負極２との間にはさみ両極を貼りあわせたものを素電池とした。
この素電池を１０対重ね、正極集電体４、負極集電体５のそれぞれの端部に接続した集電タブを、正極同士、負極同士スポット溶接することによって、各電池を電気的に並列に接続して一つの組電池を形成した。
これをアルミラミネートシートより作製した袋に入れて、エチレンカーボネートとジエチルカーボネートの混合溶媒（モル比で１：１）に６フッ化リン酸リチウムを１．０（ｍｏｌ／ｄｍ3）の濃度で溶解した電解液を注液した後、熱融着で封口し電池とした。
この電池を、８００（ｍＡ）で４．２（Ｖ）になるまで室温で充電した。
充電終了後、電池の中心部分に直径２．５（ｍｍ）の鉄釘を刺し、電池温度の測定を行った。
第２図は電極、この電極を用いた電池の特性を示した表図であり、詳しくは実施例１の電極（ここでは正極）、比較例１の電極（ここでは正極）の体積固有抵抗、体積固有抵抗の変化率、実施例１の電極を用いた電池、比較例１の電極を用いた電池の放電容量を示した表図である。
図において、比較例１における正極は実施例１の正極の製造方法において、電子導電性材料として人造黒鉛ＫＳ−６（ロンザ社製）を用いて正極を製造したものである。
なお、比較例１における負極は実施例１に示した負極の製造方法により製造したものである。
また図において、抵抗変化率とは、ＰＴＣの機能が発現した後の体積固有抵抗をＰＴＣの機能が発現する前の体積固有抵抗で除した値としたものである。
図に示すように、比較例１では電子導電性材料は樹脂を含まないため、実施例１に比べ抵抗変化率が小さいことが解る。
また、放電容量は、比較例１と実施例１とは同程度であるのが分かる。
実施例１には電極中、特に正極１の正極活物質層６の電子導電性材料９に樹脂を含むので、ＰＴＣの機能が発現した後の抵抗が発現する前の抵抗の５０倍にも増加しているのが解る。
従って、この電極を用いて電池を構成すると、電池の内部の温度が所定の温度よりも大きくなるとＰＴＣの機能が発現するため、短絡電流の増加を抑制し、電池の安全性、信頼性が更に向上する。
実施例１では抵抗変化率が５０のものを例に説明したが、これに限定される必要はなく、抵抗変化率は１．５〜１００００程度とすれば上述の効果を得ることができる。
第３図は電極を用いた電池の特性を示す図であり、具体的には実施例１の電極を用いた電池および比較例１の電極を用いた電池に対して釘刺し試験を行ったとき、電池の温度と時間経過との関係を示すグラフ図である。
実施例１の電極を用いた電池はその温度が所定の温度付近まで上昇したとき、ＰＴＣの機能が働くため、１５０（度）付近まで温度が上昇した後、５分以内に温度が下がり始めているが、比較例１の電極を用いた電池は時間とともに温度が上昇し続ける。
実施例１と比較例１とを比較すると、実施例１には電極中、特に正極１の正極活物質層６の電子導電性材料９に樹脂を混合したので、この電極を用いて電池を構成すると、電池の内部の温度が所定の温度よりも大きくなるとＰＴＣの機能が発現し、電池の温度が１６０（度）を越える前に短絡電流の増加を抑制するため、電池の安全性、信頼性が更に向上する。
第４図は電極を用いた電池の特性を示す図であり、具体的には実施例１の電極を用いた電池および比較例２の電極を用いた電池に対して釘刺し試験を行ったとき、電池の温度と時間経過との関係を示す図である。
図において、比較例２の正極は、実施例１の正極の製造方法において、電子導電性材料９として、カーボンブラックとポリプロピレン樹脂（融点：１６８（度））を含むペレットを用いて正極を製造したものである。
なお、比較例２における負極は実施例１に示した負極の製造方法により製造したものである。
図に示すように比較例２では、電子導電性材料９に含まれる樹脂に融点が１６８（度）であるポリプロピレン樹脂を用いたので、この樹脂を含む電極を用いて電池を構成したとき、ＰＴＣの機能が発現する温度は１６０（度）を越えてしまうと考えられる。
これに対し、実施例１では融点が１６０（度）よりも低いポリエチレンを樹脂としたので、電池の温度が１６０（度）を越える前に短絡電流の増加を抑制するため、電池の安全性、信頼性が更に向上する。
実施例１の電極を用いた電池は温度上昇時にＰＴＣの機能が働いて、１５０（度）付近まで温度が上昇した後、温度が下がり始めているが、比較例２の電極を用いた電池はＰＴＣの機能の発現する温度が高く、２００（度）以上になっても温度が上昇し続ける。
これは電子導電性材料に含まれる樹脂（ここではポリプロピレン樹脂）の融点が１６０（度）よりも高いためである。
よって、電子導電性材料９に含まれる樹脂はその融点が９０（度）〜１６０（度）の範囲にあるものを選択すれば、電池の性能の低下を起こさず、かつＰＴＣの機能が発現する温度を１６０（度）よりも小さくすることができる。
第５図は電極、この電極を用いた電池の特性を示す表図であり、具体的には電極の体積固有抵抗、温度上昇時の抵抗変化率、電池の２Ｃ（Ｃ：時間率）における放電容量の値、および釘刺し試験開始１０分後の電池の温度を示す表図である。
図において、比較例３とは実施例１の正極の製造方法において、電子導電性材料９として、カーボンブラックを３８重量部、ポリエチレンを６２重量部の割合で含むペレットを用いて電極（ここでは正極１）を製造するとともに、この電極を用いて電池を製造したものである。
なお、比較例３において、負極の製造方法は実施例１に同じである。
また、比較例４とは実施例１の正極の製造方法において、電子導電性材料として、カーボンブラックを７１重量部、ポリエチレンを２９重量部の割合で含むものを用いて電極（ここでは正極１）を製造するとともに、この電極を用いて電池を製造したものである。
なお、比較例４において、負極の製造方法は実施例１に同じである。
図に示すように、比較例３は実施例１に比べ抵抗変化率は大きいが、電極の抵抗値が高く、放電容量が低くなった。
また、比較例４は実施例１に比べ放電容量は高いが、カーボンブラックの割合が多すぎてＰＴＣの機能の働きが不十分なため、釘刺し試験を行うと１０分後の温度は非常に高くなった。
従って、電子導電性材料９に含まれる導電性充填材の割合を変えることにより、電極の抵抗変化率、および電池の放電容量を適切な値にすることが可能となる。
特に電極（ここでは正極１）に含まれる導電性充填材の割合を４０重量部〜７０重量部とすることにより、正常時（ＰＴＣの機能が発現する前）の電極の抵抗を低くするともに、電極の抵抗変化率を高いものにできるとともに、この電極を用いて電池を構成したときの放電容量を高いものにすることができる。
更には電子導電性材料に含まれる導電性充填材の割合を５０重量部〜６８重量部とすることにより、第５図に示した電極の特性、電池の特性を更に望ましいものにすることができる。
第６図は電極、この電極を用いた電池の特性を示す図であり、具体的には電子導電性材料の割合と電極の体積固有抵抗との関係および電子導電性材料の割合と放電容量との関係を示すグラフ図であり、詳しくは電池の正極活物質層の全固形分１００重量部に対する電子導電性材料の割合と電極の体積固有抵抗（図中（ａ））との関係および電池の正極活物質層の全固形分１００重量部に対する電子導電性材料の割合と放電容量との関係（図中（ｂ））示す図である。
図に示すように、電子導電性材料９の割合が０．５重量部以下であると正常時の電極自体の抵抗値が高すぎて放電容量が低く、電池の性能の面で問題がある。
また、１５重量部以上になると活物質量が減ることにより放電容量は低くなる。
従って、電極に含まれる電子導電性材料９の割合は０．５重量部〜１５重量部とすることにより、正常時における電極の抵抗を低くし、かつこの電極を用いた電池の放電容量を高くすることができる。
更に好ましくは、電極（ここでは正極）の全固形分１００重量部に対する電子導電性材料の割合を０．７重量部〜１２重量部、更に好ましくは、１重量部〜１０重量部とすることにより上述の特性をより望ましいものにできる。
第７図は電子導電性材料の粒径と電極の抵抗との関係（図中（ａ））及び電子導電性材料の粒径と放電容量との関係を示す図（図中（ｂ））である。
電子導電性材料９の粒径が０．０５（μｍ）以下になると、電子導電性材料９の充填率が下がり、正極活物質層６の単位体積当たりの電子導電性材料９の体積が増加すること、つまり正極活物質層６の単位体積当たりの正極活物質重量が減少することを意味する。
このため、電子導電性材料９の粒径が０．０５（μｍ）以下になると、放電容量が低くなる。
また、電子導電性材料９の粒径が１００（μｍ）以上の粒径になると、電極自体の抵抗値が高く、放電容量は低くなる。
従って、電子導電性材料９の平均粒径を０．０５（μｍ）〜１００（μｍ）とすれば正常時の電極の抵抗を低く、かつ放電容量を高くすることができる。
また、電子導電性材料９の平均粒径を０．１（μｍ）〜５０（μｍ）、更に好ましくは０．５（μｍ）〜２０（μｍ）とすれば、電子導電性材料９の体積分率、電極自体の体積固有抵抗、および放電容量をより望ましいものにすることができる。
第８図は、電子導電性材料の平均粒径、電極の抵抗、及び電池の放電容量を示す表図である。
図において、比較例５とはボールミル方式により電子導電性材料を粉砕したものを用いて電極（ここでは正極１）を製造したものである。
比較例５において、負極の製造方法は実施例１に同じである。
比較例５はボールミル方式により電子導電性材料を粉砕しているため、得られる電子導電性材料９の粒子の平均粒径が大きくなり、その結果電極の体積固有抵抗が高く、放電容量が小さいことがわかる。
従って、正常時の電極の抵抗をより小さく、かつ電池の放電容量をより高くするためには、ジェットミル方式により電子導電性材料を粉砕するのが望ましいことが分かる。
実施例２．
実施例２は実施例１において、正極活物質ペーストをアルミニウム箔上に塗布し、これを８０（度）で乾燥させた後、１３５（度）で０．５（ｔｏｎ／ｃｍ2）で３０分加圧し、電極（ここでは正極１）を製造したことを特徴とする。
実施例２において、負極の製造方法は、実施例１に同じである。
第９図は、実施例２の電極、この電極を用いた電池の特性を示す表図である。
図に示すように実施例２では乾燥させた正極活物質ペーストをプレスするとき、電子導電性材料９に含まれる樹脂の融点付近の温度でプレスするため、正極集電体４と正極活物質層６との密着性を高くすることができ、正極集電体４と正極活物質層６との間の接触抵抗を低くすることができる。
更に、電子導電性材料９が変形し、正極活物質８の間にゆきわたるとともに、電子導電性材料９同士のつながりが良くなるので、集電ネットワークが更に多く形成され、正常時の正極活物質層６の抵抗を低くすることができる。
これにより、正常時における電極（ここでは正極１）の抵抗を更に低くすることができる。
これは、乾燥させた正極活物質ペーストをプレスするときの温度または圧力（ここでは面圧）を調節することにより、得られる電極の抵抗の値を調節できることを意味する。
特に乾燥させた正極活物質ペーストをプレスするときの温度を電子導電性材料に含まれる樹脂の融点または融点付近の温度とすると、圧力をある程度小さくしたとしても、樹脂の融点付近の温度でプレスしているので、得られる電極の正常時での体積固有抵抗の値を小さくすることができる。
実施例３．
（正極の製造方法）
室温における体積固有抵抗が０．２（Ω・ｃｍ）、動作温度１３５（度）における体積固有抵抗が５００（Ω・ｃｍ）の特性を有する電子導電性材料（例えばカーボンブラックとポリエチレンとが所定の割合で有するペレット）をジェットミル方式により粉砕し、平均粒径９．０（μｍ）の電子導電性材料の微粒子を得た。
この電子導電性材料の微粒子を４．５重量部、導電助剤として人造黒鉛ＫＳ−６（ロンザ社製）を１．５重量部、活物質（例えばＬｉＣｏＯ２）を９１重量部、バインダー（例えばＰＶＤＦ）を３重量部含むものを分散媒であるＮＭＰに分散させることにより調整した正極活物質ペーストを得た。
次に、上述の正極活物質ペーストを、正極集電体４となる厚さ２０（μｍ）の金属膜（ここではアルミニウム箔）上にドクターブレード法にて塗布した。さらに、８０（度）で乾燥した後、所定の温度（例えば室温）でかつ所定の面圧（例えば２（ｔｏｎ／ｃｍ2））でプレスし、正極集電体４の上に厚さ約１００（μｍ）の正極活物質層６を形成した正極１を得た。また、実施例３の負極の製造方法は実施例１に同じである。
第１０図は、電極、この電極を用いた電池の特性を示す図であり、具体的には実施例１の電極の体積固有抵抗、実施例１の電極を用いた電池の放電容量、釘差し試験開始１０分後の電池の温度および実施例３の電極の体積固有抵抗、実施例３の電極を用いた電池の放電容量、釘差し試験開始１０分後の電池の温度を示す表図である。
実施例１と比較して、実施例３の電極は放電容量が実施例１とほぼ同様の値を示した。
つまり、体積固有抵抗が高い電子導電性材料を用いたときでも、導電助剤を加えることにより、正常時の電極の体積固有抵抗を低くするとともに、この電極を用いた電池の放電容量を高いものにすることができる。
ここで、導電助剤を黒鉛（ここでは人造黒鉛ＫＳ−６（ロンザ社製））としたがこれに限定する必要はなく、アセチレンブラック、ランプブラック等のカーボンブラックといったように電極の電子導電性を高めるものであって、温度の上昇に伴いその抵抗がほとんどど変化しない物質（または電子導電性を高めるものであってＰＴＣの機能を有しない物質）であれば、導電助剤は何であってもよい。
実施例４．
実施例４の電池の正極は実施例１の正極の製造方法において、電子導電性材料を複合粉砕方式により粉砕した電子導電性材料の微粒子を更にジェットミル方式により粉砕し得られる電子導電性材料の微粒子を用いて、電極（ここでは正極１）を形成したことを特徴とする。
実施例４の負極の製造方法は実施例１に同じである。
第１１図は実施例４の電極（ここでは、正極１）に用いる電子導電性材料の平均粒径を示す表図である。
図によれば、実施例１に比べ実施例４の方が平均粒径が小さいのが分かる。
これは、複合粉砕方式により、予め電子導電性材料の粒径を小さくした後、更にジェットミル方式により電子導電性材料を粉砕したので、得られる電子導電性材料の粒径、粒径のばらつきをともに小さくできるとともに、電子導電性材料の粉砕に要する時間を短くすることもできる。
よって、この電子導電性材料を用いて電極を製造すると、柔軟性が高く、加工の容易な電極を得ることができる。
また、この実施例４では正極を例に説明をしたが、負極に適用しても同様の効果を奏する。
実施例５．
実施例５の正極は、実施例４において、電子導電性材料を冷却しながら複合粉砕方式により粉砕し、得られる電子導電性材料の微粒子を用いて電極（ここでは正極１）を形成したことを特徴とするものである。
実施例５の負極の製造方法は実施例１に同じである。
第１２図は複合粉砕方式により粉砕する前の電子導電性材料の粒径、複合粉砕方式により粉砕した後の電子導電性材料の粒径を示す表図である。
図によれば、複合粉砕方式により電子導電性材料を粉砕するとき、電子導電性材料を冷却しながら粉砕した方が粒径をより小さくすることができる。
従って電子導電性材料を冷却しながら粉砕すれば、得られる電子導電性材料の粒径、粒径のばらつきを更に小さくできるので、柔軟性が更に高く、加工が更に容易な電極を得ることができる。
実施例６．
実施例６の電極は、少なくとも２種類の電子導電性材料を有することを特徴とする。
ここでは、正極１の正極活物質層６が２種類の電子導電性材料を有するものを例に説明する。
以下に実施例６の正極の製造方法、負極の製造方法を説明する。
（正極の製造方法）
第１の電子導電性材料（例えば、カーボンブラックを７０重量部、ポリエチレンを３０重量部を含むペレット）をジェットミル方式により細かく粉砕することにより、第１の電子導電性材料の微粒子を得た。
また、第２の電子導電性材料（例えば、炭化ダングステンを９０重量部、ポリエチレンを１０重量部を含むペレット）をジェットミル方式により細かく粉砕することにより、第２の電子導電性材料の微粒子を得た。
次に、この第１の電子導電性材料の微粒子を４．２重量部、第２の電子導電性材料の微粒子を１．８重量部、正極活物質（例えばＬｉＣｏＯ2）を９１重量部、バインダー（例えばＰＶＤＦ）を３重量部を分散媒であるＮＭＰに分散させることにより調整することにより、正極活物質ペーストを得た。
次に、上述の正極活物質ペーストを、正極集電体４となる厚さ２０（μｍ）の金属膜（ここではアルミニウム箔）上にドクターブレード法にて塗布した。さらに、８０（度）で乾燥した後、所定の温度（例えば室温）でかつ所定の面圧（例えば２（ｔｏｎ／ｃｍ2））でプレスし、正極集電体４の上に厚さ約１００（μｍ）の正極活物質層６を形成した正極１を得た。
また、実施例６の負極の製造方法は実施例１に同じである。
実施例６の電極、この電極を用いた電池の性能を確認するために以下に示す試験を行った。
（短絡試験）
上述の方法により得られた正極１、負極２をそれぞれ３８（ｍｍ）×６５（ｍｍ）の大きさに切断した。
ポリプロピレンシート（ヘキスト社製セルガード♯２４００）をセパレータ３とし、このセパレータ３を正極と負極の間に挟むように置き、両側から厚さ約１（ｍｍ）のテフロン板で挟んでテープでとめ、正極集電体４、負極集電体５それぞれの端部に集電タブを、超音波溶接によって取り付け、これをアルミラミネートシートにより作成した袋に入れ、エチレンカーボネートとジエチルカーボネートの混合溶媒（モル比で１：１）に６フッ化リン酸リチウムを１．０（ｍｏｌ／ｄｍ3）の濃度で溶解した電解液を注液した後、熱融着で封口し電池とした。
この電池を、８０（ｍＡ）で４．２（Ｖ）になるまで室温で充電した。充電終了後、この電池をオーブン内で昇温していき、１４５（度）において短絡させた時の電流値を測定した。
第１３図は、電極、この電極を用いた電池の特性を示す図であり、具体的には電極の体積固有抵抗値、電極の柔軟性、この電極を用いた電池の短絡電流値を示す表図である。
図において電極の柔軟性は○がかなり良く、△は程々に良いことを示すものである。
図より、実施例６では比較例１に比べ、体積固有抵抗が低く、柔軟性が高く、短絡電流も低くなることが分かる。
従って、電極（ここでは正極１の正極活物質層６）に少なくとも２種類の電子導電性材料を含むようにすれば、所定の温度よりも低い温度での抵抗が低く、柔軟性が高く、加工の容易な電極を得ることができる。
更にこの電極を用いて電池を構成すると、電池の外部または内部で短絡事故が発生し、電池の温度が上昇しても、電池内部に流れる短絡電流が減少するので、安全性が高い電池を得ることができる。
実施例６では、電極に２種類の電子導電性材料を含むものを例に説明したがこれに限定されるものではない。
要は、電極に含まれる電子導電性材料を複数種類にすれば上述の効果を得ることができる。
実施例７．
実施例７の電極の中に含まれる電子導電性材料は、少なくとも２種類の導電性充填材を有することを特徴とする。
ここでは、正極１の正極活物質層６の電子導電性材料９が２種類の導電性充填材を有するものを例に説明する。
以下に実施例７の正極の製造方法、負極の製造方法を説明する。
（正極の製造方法）
導電性充填材として、カーボンブラックと炭化タングステンを含有したもの（混合比は例えば７５重量部：２５重量部）を用い、この導電性充填材と樹脂（ここではポリエチレン）とを含むペレットを電子導電性材料とする。
この電子導電性材料を例えばジェットミル方式により粉砕し、電子導電性材料の微粒子を得た。
この電子導電性材料の微粒子を６重量部、正極活物質（例えば、ＬｉＣｏＯ2）を９１重量部、バインダー（例えばＰＶＤＦ）を３重量部含むものを分散媒（例えば、ＮＭＰ）に分散させることにより調整し、正極活物質ペーストを得た。
これ以降の正極の製造方法は実施例１に同じである。
また、負極の製造方法は実施例１に同じである。
実施例７の電極、この電極を用いた電池の性能を確認するために試験を行った。
第１４図は、電極、この電極を用いた電池の特性を示す表図であり、具体的には電極の体積固有抵抗値、電極の柔軟性、この電極を用いた電池の短絡電流値を示す表図である。
図において電極の柔軟性は○がかなり良く、△は程々に良いことを示すものである。
図より、実施例７では比較例１に比べ、正常時における電極の体積固有抵抗が低くなる。また、電極の柔軟性が高くなる。また実施例７の電極を用いた電池の短絡電流の値も低くなることが分かる。
従って、電子導電性材料９が少なくとも２種類の導電性充填材を含むようにすれば、所定の温度よりも低い温度での抵抗が低く、柔軟性が高く、加工の容易な電極を得ることができる。
更にこの電極を用いて電池を構成すると、電池の外部または内部で短絡事故が発生し、電池の温度が上昇しても、電池内部に流れる短絡電流が減少するので、安全性が高い電池を得ることができる。
実施例７では、電子導電性材料９は、２種類の導電性充填材を含むものを例に説明したがこれに限定されるものではない。
要は、電子導電性充填材９は複数種類の導電性充填材を有するようにすれば、上述の効果を得ることができる。
実施例８．
実施例８の電極は、種類の異なる樹脂を有することを特徴とする。
ここでは、正極１の正極活物質層６の電子導電性材料９が２種類の樹脂を有するものを例に説明する。
以下に実施例８の正極の製造方法、負極の製造方法を説明する。
（正極の製造方法）
樹脂として、ポリエチレンとポリプロピレンを所定の割合で混合したもの（例えば混合比は７５重量部：２５重量部）を用い電子導電性材料を構成したこと以外は実施例１に同じである。
また、実施例８の負極の製造方法は実施例１に同じである。
実施例８の電極、この電極を用いた電池の性能を確認するために試験を行った。
第１５図は、電極、この電極を用いた電池の特性を示す図であり、具体的には電極の体積固有抵抗値、電極の柔軟性、この電極を用いた電池の短絡電流値を示す表図である。
図より、実施例８では比較例１に比べ、正常時の電極の体積固有抵抗が低くなる。また実施例８の電極を用いた電池の短絡電流値も低くなることが分かる。
従って、電子導電性材料９が少なくとも２種類の樹脂を含むようにすれば、所定の温度よりも低い温度での抵抗が低い電極を得ることができる。
更にこの電極を用いて電池を構成すると、電池の外部または内部で短絡事故が発生し、電池の温度が上昇しても、電池内部に流れる短絡電流が減少するので、安全性が高い電池を得ることができる。
実施例８では、電子導電性材料９は、２種類の樹脂を有するものを例に説明したがこれに限定されるものではない。
電子導電性充填材９は複数種類の樹脂を有するような構成にしても上述の効果を奏する。
またこれらの樹脂のうち、少なくとも１つの樹脂の融点が９０（度）〜１６０（度）の間にあれば、この温度範囲においてＰＴＣの機能が発現する。
従って、この樹脂以外の樹脂はその融点が上述の範囲にないものを用いても構わない。
また、複数種類の樹脂の割合を変えることにより、ＰＴＣの機能が発現する温度を任意に調節することが可能となる。
実施例９．
実施例９の電極は、活物質として、マンガン系酸化物を用いて電極を構成したことを特徴とする。
ここでは、正極１に用いる正極活物質８としてＬｉＭｎ2Ｏ4を用いて正極１を製造し、この正極１を用いて電池を構成したことを特徴とする。
実施例９の正極の製造方法は、実施例１の正極の製造方法において、正極活物質としてＬｉＭｎ2Ｏ4を用いたこと以外は実施例１に同じである。
また、実施例９の負極の製造方法は実施例１に同じである。
実施例９の電極、電池の性能を確認するために短絡試験を行った。
第１６図は実施例１の電極を用いた電池、実施例９の電極を用いた電池の短絡電流値を示す表図である。
図に示すように活物質（ここでは正極活物質８）として、ＬｉＭｎ2Ｏ4を用いても短絡電流の値は、実施例１と同程度となるのが分かる。
従って、実施例９の電極を用いて電池を構成すると、電池の外部または内部で短絡事故が発生し、電池の温度が上昇しても、電池内部に流れる短絡電流が減少するので、安全性が高い電池を得ることができる。
実施例１０．
実施例１０の電極は、活物質として、鉄系酸化物を用いて電極を構成したことを特徴とする。
ここでは、正極に用いる正極活物質としてＦｅ2（ＳＯ4）3を用いて正極を形成し、この正極を用いて電極を形成したことを特徴とする。
実施例１０の正極の製造方法は、実施例１の正極の製造方法において、正極活物質として、Ｆｅ2（ＳＯ4）3を用いたこと以外は実施例１に同じである。
また、実施例１０の負極の製造方法は実施例１に同じである。
実施例１０の電極、この電極を用いた電池の性能を確認するために短絡試験を行った。
第１７図は実施例１の電極を用いた電池、実施例１０の電極を用いた電池の短絡電流値を示す表図である。
図に示すように活物質（ここでは正極活物質８）として、Ｆｅ2（ＳＯ4）3を用いても、短絡電流の値は実施例１と同程度となるのが分かる。
従って、実施例１０の電極を用いて電池を構成すると、電池の外部または内部で短絡事故が発生し、電池の温度が上昇しても、電池内部に流れる短絡電流が減少するで、安全性が高い電池を得ることができる。
実施例１１．
第１８図は、上述した電極、電池をリチウムイオン二次電池に適用したものの一例を示す図であり、具体的にはの円筒型のリチウムイオン二次電池の構造を示す断面図である。
図において、２００は負極端子を兼ねるステンレス製などの外装缶、１００はこの外装缶２００内部に収納された電池体であり、電池体１００は正極１、セパレータ３および負極２を渦巻状に巻いた構造になっている。
電池体１００の正極１は上述した正極の構成を有する。
このようにすることにより、電池の外部または内部における短絡により電流が増大し、電池もしくは電極の温度がある程度以上に上昇した場合において正極１（特に正極活物質層）自体の抵抗が大きくなるので、電池内部に流れる電流が減少する。
従って、この電極を用いて電池を構成したとき、電池の安全性は飛躍的に向上し、厳しい条件下での短絡、逆充電あるいは過充電等の異常時においても電池の安全性が保たれるという効果を奏する。
ここでは、正極１が温度の上昇に伴いその抵抗が大きくなるものを例に説明したが、負極２（特に負極活物質層）に樹脂および導電性充填材を含有する電子導電性材料を含むようにすれば、負極２が温度の上昇に伴いその抵抗が大きくなるので、上述の効果と同じ効果を得ることが可能となる。
また、上述した実施例に示した電極、電池は、有機電解液型、固体電解質型、ゲル電解質型のリチウムイオン二次電池のみならず、リチウム／二酸化マンガン電池などの一次電池、その他二次電池において用いることが可能である。
更には、水溶液系一次電池、二次電池についても有効である。更には、電池形状によらず、積層型、及び巻き型、ボタン型などの一次、二次電池にも用いることが可能である。
産業上の利用可能性
この発明による電極、電池は、有機電解液型、固体電解質型、ゲル電解質型のリチウムイオン二次電池のみならず、リチウム／二酸化マンガン電池などの一次電池、その他二次電池において用いることが可能である。
更には、水溶液系一次電池、二次電池についても有効である。更には、電池形状によらず、積層型、及び巻き型、ボタン型などの一次、二次電池にも用いることが可能である。Technical field
The present invention relates to an electrode, a method for manufacturing the electrode, and a battery using the electrode, and more specifically, an electrode whose resistance increases with an increase in temperature, a method for manufacturing the electrode, and the electrode. It is related to the battery.
Background art
In recent years, with the development of electronic devices, the capacity and the output density of batteries used as a power source have been increasing. Lithium ion secondary batteries are attracting attention as batteries that satisfy these requirements. Although this lithium ion secondary battery has the advantage of high energy density, a sufficient measure for safety is required due to the use of a non-aqueous electrolyte.
Conventionally, as countermeasures for safety, it has been proposed to release an increase in internal pressure by a safety valve, or to incorporate a PTC element that interrupts current by increasing resistance in response to heat generated by an external short circuit, etc.
For example, as disclosed in Japanese Patent Application Laid-Open No. 4-328278, a method of attaching a safety valve and a PTC element to a positive electrode cap portion of a cylindrical battery is known. However, when the safety valve is operated, moisture in the atmosphere may enter the battery, and if lithium is present in the negative electrode, an exothermic reaction may occur.
On the other hand, the PTC element cuts off the external short circuit, and there is no harmful effect caused by the operation. For example, the PTC element can be a safety component that operates first when a battery abnormality occurs by designing the PTC element to operate when the battery reaches a temperature of 90 degrees or more due to an external short circuit.
Since the conventional lithium secondary battery has the above-described configuration, it has the following problems.
The conventional lithium secondary battery cannot suppress an increase in the short-circuit current when a short circuit occurs inside the lithium secondary battery and the temperature rises.
When a short circuit occurs inside the lithium secondary battery and the temperature rises, the separator made of polyethylene or polypropylene, which is disposed between the positive electrode and the negative electrode, is softened or melted to close the pores of the separator, thereby separating the separator. The separator is expected to have a function of reducing the ionic conductivity of the separator portion by extruding or enclosing the non-aqueous electrolyte contained therein and reducing the short-circuit current.
However, the separator away from the heat generating portion does not necessarily melt. Further, when the temperature further rises, the separator melts and flows, so that the function of electrically insulating the positive and negative electrodes is lost, leading to a short circuit.
In particular, in the case of a lithium ion secondary battery, the negative electrode is a slurry containing a negative electrode active material such as graphite, a binder such as PVDF (polyvinylidene fluoride), and a solvent on a base material such as a copper foil serving as a current collector. Is applied and dried to form a thin film. Similarly, the positive electrode is formed as a thin film on a base material such as an aluminum foil serving as a current collector.
However, the positive electrode is LiCoO 2 And a positive electrode active material, a binder, and a conductive additive.
The conductive auxiliary agent is for increasing the electronic conductivity of the positive electrode when the positive electrode active material has poor electronic conductivity. Examples of the conductive assistant include carbon black (for example, acetylene black) and graphite (for example, KS-6).
In such a battery, when the battery temperature rises above the temperature at which the separator melts and flows due to an internal short circuit or the like, a large short-circuit current is generated between the positive electrode and the negative electrode at the portion where the separator flows. There is a problem that the temperature of the battery further rises and the short-circuit current further increases.
The present invention has been made to solve the above-described problems, and an object thereof is to obtain an electrode whose resistance increases as the temperature rises, a method for manufacturing the electrode, and a battery using the electrode. .
Disclosure of the invention
The first electrode according to the present invention includes an active material,
An electrode having an electronically conductive material in contact with the active material,
The electronic conductive material contains a conductive filler and a resin, and is configured to increase its resistance with increasing temperature. The particle diameter of the electronic conductive material is 0.05 (μm) to 100 (μm).
According to this, since the electronic conductive material contains a conductive filler and a resin, and the temperature rises and the resistance increases, the current flowing through the electrode when the temperature rises. Can be suppressed. Further, since the particle diameter of the electron conductive material is set to 0.05 (μm) to 100 (μm), the resistance of the electrode before the phenomenon in which the rate of change in resistance of the electrode increases is reduced, and this electrode is The discharge capacity when applied to a battery can be increased.
The second electrode according to the present invention is characterized in that an electron conductive material resin having a melting point in the range of 90 (degrees) to 160 (degrees) is used.
According to this, since the resin of the electronic conductive material is a resin having a melting point in the range of 90 (degrees) to 160 (degrees), the electronic conductive material is in the range of 90 (degrees) to 160 (degrees). The resistance increases near a predetermined temperature.
The third electrode according to the present invention comprises an electronic conductive material in an amount of 0.5 to 15 parts by weight with respect to 100 parts by weight of the total solid content of the active material layer.
According to this, since the material containing 0.5 to 15 parts by weight of the electronic conductive material is used, the resistance of the electrode before the phenomenon in which the rate of change in resistance of the electrode increases can be lowered.
The fourth electrode according to the present invention is characterized in that the ratio of the conductive filler of the electronic conductive material is 40 to 70 parts by weight.
According to this, since the ratio of the conductive filler of the electronic conductive material is 40 parts by weight to 70 parts by weight, the rate of change of the resistance of the electrode near a predetermined temperature is large, and this electrode is applied to the battery. In this case, the discharge capacity of the battery can be increased.
A fifth electrode according to the present invention is characterized in that the conductive filler is a carbon material or a conductive non-oxide.
According to this, since the conductive filler is carbon or conductive non-oxide, the conductivity of the electrode can be increased.
A sixth electrode according to the present invention is characterized in that the electrode enhances the electronic conductivity and includes a conductive assistant whose resistance hardly changes as the temperature rises.
According to this, the sixth electrode enhances the electronic conductivity, and includes a conductive additive whose resistance hardly changes as the temperature rises. Therefore, the sixth electrode has a low electronic conductivity. Even if it uses, the resistance of an electrode can be adjusted to an appropriate thing.
The seventh electrode according to the present invention is characterized by containing at least two different types of electronic conductive materials.
According to this, since at least two different types of electronic conductive materials are contained, an electrode having a low resistance at a temperature lower than a predetermined temperature and a high flexibility can be obtained. When configured, when the temperature inside the battery rises above a predetermined temperature, the resistance of the electrode increases, and the current flowing inside the battery decreases, so the safety of the battery improves.
An eighth electrode according to the present invention is characterized in that the electronic conductive material contains at least two kinds of different conductive fillers.
According to this, since the electronic conductive material contains at least two different kinds of conductive fillers, an electrode having low resistance at a temperature lower than a predetermined temperature and high flexibility can be obtained. When the battery is configured using the battery, if the temperature inside the battery rises above a predetermined temperature, the resistance of the electrode increases, and the current flowing inside the battery decreases, so the safety of the battery improves.
A ninth electrode according to the present invention is characterized in that the electronic conductive material contains at least two kinds of different resins.
According to this, since the electronic conductive material contains at least two kinds of different resins, an electrode having a low resistance at a temperature lower than a predetermined temperature is obtained, and a battery is configured using this electrode. When the temperature inside the battery rises above a predetermined temperature, the resistance of the electrode increases and the current flowing inside the battery decreases, so that the safety of the battery is improved.
A first battery according to the present invention includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode,
Any one of the first electrode to the ninth electrode is used for the positive electrode or the negative electrode.
According to this, since any one of the first electrode to the ninth electrode is used for the positive electrode or the negative electrode, the resistance of the electrode increases when the internal temperature of the battery rises above a predetermined temperature, and the battery Since the current flowing inside decreases, the safety of the battery is improved.
The first electrode manufacturing method according to the present invention comprises:
(A) A step of pulverizing an electronic conductive material containing a conductive filler and a resin
(B) A step of producing an active material paste by dispersing the pulverized electronic conductive material and the active material.
(C) A step of pressing the dried active material paste at a predetermined temperature and a predetermined pressure.
It has the process which becomes.
According to this, since the steps (a) to (c) are provided, the connection between the electronic conductive materials is improved, so that the resistance of the electrode at a temperature lower than a predetermined temperature can be reduced.
The second electrode manufacturing method according to the present invention is characterized in that, in the first electrode manufacturing method, the predetermined temperature is a melting point of the resin or a temperature near the melting point.
According to this, since the predetermined temperature is the melting point of the resin or a temperature near the melting point, the connection between the electronic conductive materials is further improved, and the resistance of the electrode at a temperature lower than the predetermined temperature is further reduced. Can do.
The third electrode manufacturing method according to the present invention is the first electrode manufacturing method, wherein the step of pulverizing the electronic conductive material containing the conductive filler and the resin is performed by supersonic flow. The electronic conductive material is crushed by applying a conductive material to a wall surface or causing the electronic conductive material to collide with each other.
According to this, the electron conductive material placed on a supersonic flow is applied to the wall surface or the electron conductive material collides with each other to pulverize the electron conductive material. When an electrode is manufactured using this electronic conductive material, the resistance of the electrode at a temperature lower than a predetermined temperature can be further reduced.
The fourth electrode manufacturing method according to the present invention is the first electrode manufacturing method, wherein the step of pulverizing the electronic conductive material containing the conductive filler and the resin includes a shearing force applied to the electronic conductive material. The above-mentioned electronic conductive material is pulverized by applying a grinding force and an impact force in combination.
According to this, since the electronic conductive material is pulverized by applying a shearing force, a grinding force and an impact force to the electronic conductive material in combination, an electronic conductive material with a small variation in particle size can be obtained. When an electrode is manufactured using this electronic conductive material, an electrode with high flexibility can be obtained, so that the electrode can be easily processed.
A fifth electrode manufacturing method according to the present invention is characterized in that, in the fourth electrode manufacturing method, the electron conductive material is pulverized while being cooled.
According to this, since the electronic conductive material is pulverized while being cooled, it is possible to obtain an electronic conductive material with a smaller variation in particle diameter. When an electrode is manufactured using this electronic conductive material, flexibility is obtained. Since a higher electrode can be obtained, processing of the electrode is further facilitated.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the configuration of the battery, FIG. 2 is a table showing the volume resistivity of the electrode, the rate of change in resistance, and the discharge capacity of the battery, and FIG. 3 is the elapsed time when the nail penetration test was conducted. 4 is a graph showing the relationship between the battery temperature and the battery temperature, FIG. 4 is a graph showing the relationship between the elapsed time and the battery temperature when the nail penetration test was performed, and FIG. 5 is the electrode volume resistivity and the temperature rise. FIG. 6 is a table showing the rate of change in resistance, the discharge capacity of the battery, and the temperature of the battery 10 minutes after the start of the nail penetration test, FIG. 6 shows the relationship between the ratio of the electronic conductive material and the resistance value of the electrode, and the electronic conductive material FIG. 7 is a graph showing the relationship between the particle size of the electronic conductive material and the volume resistivity of the electrode, and the relationship between the particle size of the electronic conductive material and the discharge capacity. Fig. 8 shows the average particle diameter of the electroconductive material, the resistance of the electrode, and the discharge capacity of the battery. Fig. 9 is a table showing the porosity, volume resistivity, and discharge capacity of the electrode. Fig. 10 is the electrode volume resistivity, battery discharge capacity, and battery temperature 10 minutes after the start of the nail penetration test. Table, FIG. 11 is a table showing the average particle diameter of the electronic conductive material used for the electrode, FIG. 12 is the particle diameter of the electronic conductive material before pulverization by the composite pulverization method, and after pulverization by the composite pulverization method FIG. 13 is a table showing the volume resistivity of the electrode, the flexibility of the electrode, the flexibility of the electrode, the short-circuit current value of the battery, and FIG. 14 is the volume resistivity of the electrode. Table showing the flexibility of the electrode and the short circuit current value of the battery, FIG. 15 is a table showing the volume resistivity of the electrode, the flexibility of the electrode and the short circuit current value, and FIG. 16 shows the short circuit current value of the battery. Table, FIG. 17 is a table showing the short circuit current value of the battery, FIG. 18 is a diagram showing an example of a cylindrical battery A.
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a view for explaining a battery of the present invention, and in detail, is a longitudinal sectional view of the battery.
In the figure, 1 is a positive electrode, 2 is a negative electrode, and 3 is a separator provided between the positive electrode 1 and the negative electrode 2.
The positive electrode 1 has a positive electrode current collector 4 and a positive electrode active material layer 6.
The negative electrode 2 has a negative electrode current collector 5 and a negative electrode active material layer 7.
The positive electrode 1 is obtained by forming a positive electrode active material layer 6 on the surface of a metal film (for example, a metal film such as aluminum) to be a positive electrode current collector 4.
The negative electrode 2 is obtained by forming a negative electrode active material layer 7 obtained by forming a negative electrode active material such as carbon particles with a binder on a metal film (for example, a metal film such as copper) serving as the negative electrode current collector 5.
The separator 3 holds, for example, an electrolytic solution containing lithium ions.
The positive electrode active material layer 6 includes a positive electrode active material 8, an electronic conductive material 9, and a binder 10.
The positive electrode active material 8 is, for example, a cobalt-based oxide, a manganese-based oxide, an iron-based oxide, or the like.
The cobalt-based oxide is, for example, LiCoO. 2 Crystal or LiCoO 2 In the crystal, some Co atoms are replaced with transition metal atoms (for example, Ni atoms, Mn atoms, etc.).
The manganese-based oxide is, for example, LiMnO. 2 , LiMn 2 O Four , LiMyMn 2 -YO Four (M: Cr, Co, Ni, etc.).
Examples of iron-based oxides include LiFeO. 2 , Li Five FeO Four , Fe 2 (SO Four ) Three It is.
Since the positive electrode active material 8 and the electronic conductive material 9 are bonded together by the binder 10, some of them are in contact with each other.
The positive electrode active material 8 is in the form of particles, and the electronic conductive material 9 is in the form of particles having a shape smaller than that of the positive electrode active material 8.
The electronic conductive material 9 contains, for example, a conductive filler and a resin.
The electronic conductive material 9 has a characteristic that its resistance increases as the temperature rises. Especially, the rate of change of the resistance value is around a predetermined temperature in the range of 90 (degrees) to 160 (degrees). It has a PTC characteristic that increases and thereby increases its resistance (hereinafter, this characteristic is referred to as PTC (Positive Temperature Coefficient)).
Examples of the conductive filler include a carbon material and a conductive non-oxide.
Examples of the carbon material include carbon black, graphite, and carbon fiber.
Examples of carbon black include acetylene black, furnace black, lamp black, thermal black, and channel black.
Examples of the conductive non-oxide include metal carbide, metal nitride, metal silicide, and metal boride.
Examples of metal carbides include TiC, ZrC, VC, NbC, TaC, and Mo. 2 C, WC, B Four C, Cr Three C 2 Etc.
Examples of the metal nitride include TiN, ZrN, VN, NbN, TaN, and Cr. 2 N etc.
The metal boride is, for example, TiB 2 , ZrB 2 , NbB 2 , TaB 2 CrB, MoB, WB, etc.
Examples of the resin include high-density polyethylene (melting point: 130 (degrees) to 140 (degrees)), low-density polyethylene (melting point: 110 (degrees) to 112 (degrees)), polyurethane elastomer (melting point: 140 (degrees)). ˜160 (degrees)), polyvinyl chloride (melting point: about 145 (degrees)) and the like, and these have a melting point in the range of 90 (degrees) to 160 (degrees).
In the electronic conductive material 9, the temperature at which the PTC function develops depends on the melting point of the resin contained in the electronic conductive material 9. Therefore, the temperature at which the PTC function develops can be set to 90 by changing the resin material or type. It is possible to adjust the temperature between (degrees) and 160 (degrees).
In addition, if the resin contained in the electronic conductive material 9 is a crystalline resin, the rate of change in resistance near the temperature at which the PTC function of the electronic conductive material 9 is exhibited can be further increased.
This PTC characteristic may be reversible so that it can be expressed twice or more times, or reversible so that it does not return to the original resistance value when the temperature is lowered once the PTC function has been developed. There may be no.
Although it is preferable from the viewpoint of ensuring safety that the temperature at which the function of this PTC is expressed is 90 (degrees) or less, the resistance value of the electrode increases in a temperature range in which the battery is normally used. The battery performance deteriorates in the load factor characteristics and the like.
Further, when the temperature at which the PTC function is developed exceeds 160 (degrees), the internal temperature of the battery rises to this temperature, which is not preferable from the viewpoint of safety.
Therefore, it is desirable to design the electronic conductive material 9 so that the temperature at which the PTC function is exhibited is in the range of 90 (degrees) to 160 (degrees).
Since the temperature at which the PTC function is exhibited depends on the melting point of the resin, the resin having a melting point in the range of 90 (degrees) to 160 (degrees) is selected.
In the electronic conductive material 9, the magnitude of the resistance of the electrode at normal time (that is, before the PTC function is manifested) is adjusted by changing the ratio of the electronic conductive material 9 to the entire positive electrode active material layer 6. can do.
The electronic conductive material 9 has a PTC function because the resin contained therein softens, melts, and expands in volume, thereby increasing the resistance value of the electronic conductive material 9 itself.
In the positive electrode 1 of the battery of the present invention, since the electronic conductive material 9 itself contained in the positive electrode active material layer 6 has PTC characteristics, the temperature of the positive electrode 1 is higher than the temperature at which the electronic conductive material 9 exhibits the function of PTC. As the value increases, the resistance value of the positive electrode active material layer 6 increases.
Therefore, when an electrode having such characteristics (here applied to the positive electrode 1 of the battery) is applied to the battery, the current increases due to a short circuit outside or inside the battery, and the temperature of the battery or electrode rises to a certain extent. In some cases, the resistance value of the positive electrode active material layer 6 itself becomes high, so that the current flowing inside the battery is suppressed.
Therefore, when a battery is configured using this electrode, the safety of the battery is dramatically improved, and the safety of the battery is maintained even in the case of an abnormality such as a short circuit, reverse charge or overcharge under severe conditions. There is an effect.
Here, the positive electrode active material layer 6 has been described as an example having the positive electrode active material 8, the electronic conductive material 9, and the binder 10, but is not limited thereto.
For example, in the case where a material having a low electronic conductivity of the positive electrode active material 6 included in the positive electrode active material layer 6 is used, this can be compensated by adding a conductive additive to the positive electrode active material layer 6. It becomes.
Further, although the electronic conductive material 9 is in the form of particles, the shape may be a fiber-like or scaly piece. In short, as long as it has such a size that the electron conductive material 9 can be positioned between the adjacent positive electrode active materials 8, the shape thereof may be any.
Here, the configuration of the electronic conductive material including the conductive filler and the resin in the positive electrode 1, particularly the positive electrode active material layer 6, is disclosed, but the present invention is not limited to this, and the above configuration is applied to the negative electrode 2. Even if a battery is constructed using this, the same effect is obtained.
Next, an example of a manufacturing method of the positive electrode 1, an example of a manufacturing method of the negative electrode 2, and an example of a manufacturing method of a battery using the positive electrode 1 and the negative electrode 2 will be described.
(Production method of positive electrode)
A volume specific resistance at room temperature is sufficiently low, and an electronic conductive material (for example, conductive filler and resin) having a large volume specific resistance at a temperature higher than a predetermined temperature between 90 (degrees) and 160 (degrees) is predetermined. ) Is finely pulverized to obtain fine particles of an electronically conductive material.
As a method of pulverizing the electronic conductive material, there is a method of pulverizing using compressed air or an inert gas such as compressed nitrogen or argon.
As a means for specifically realizing this method, a supersonic airflow is generated by the above-described method, and in this airflow, the powders of the electronic conductive material collide with each other, or the powder in the airflow is removed. By colliding with a wall surface (not shown), the electroconductive material can be pulverized to obtain fine particles of the electroconductive material having a small particle size. Called the method).
In particular, in order to reduce the particle size of the obtained electronic conductive material, it is desirable to pulverize the electronic conductive material by a jet mill method.
As another method of pulverizing the electronic conductive material, there is a method of pulverizing the electronic conductive material by applying a shearing force, a grinding force and an impact force to the electronic conductive material in combination.
As a means for concretely realizing this method, for example, an electronic conductive material is pulverized by a concavo-convex blade of a rotor (not shown) and a stator (not shown) that rotate at high speed. Fine particles of the material can be obtained (a method for obtaining fine particles of the electronic conductive material thereby is called a composite grinding method).
Further, as another method of pulverizing the electronic conductive material, there is a method of pulverizing the electronic conductive material by putting it in a ball mill and rotating it to shear the electronic conductive material (the fine particles of the electronic conductive material thereby Is called the ball mill method).
In particular, if the electronic conductive material is pulverized by the composite pulverization method or the ball mill method and then pulverized by the jet mill method, the particle diameter of the fine particles of the obtained electronic conductive material and the variation in the particle diameter can be reduced.
Furthermore, if the electronic conductive material is pulverized while cooling, the particle diameter of the obtained electronic conductive material can be reduced.
Next, fine particles of the electron conductive material, positive electrode active material (for example, LiCoO 2 ) And a binder (for example, PVDF) were dispersed in a dispersion medium (for example, N-methylpyrrolidone (hereinafter abbreviated as NMP)) to obtain a positive electrode active material paste.
Next, the above-described positive electrode active material paste was applied on a current collector base material (for example, a metal film having a predetermined thickness) to be the positive electrode current collector 4.
Furthermore, after drying this, it pressed at predetermined temperature and predetermined surface pressure, the positive electrode active material layer 6 which has desired thickness was formed, and the positive electrode 1 was obtained.
In the manufacturing method of the electrode shown here (specifically positive electrode 1), since the pressing is performed at a predetermined temperature and a predetermined surface pressure, the adhesion between the positive electrode current collector 4 and the positive electrode active material layer 6 is improved. The contact resistance between the positive electrode current collector 4 and the positive electrode active material layer 6 is reduced.
Furthermore, since the connection between the electronic conductive materials 9 is improved, a large number of current collecting networks are formed, and the resistance of the positive electrode active material layer 6 in a normal state can be reduced.
Thereby, the resistance of the electrode at the normal time can be lowered.
That is, the resistance of the electrode to be manufactured can be adjusted by adjusting the temperature and pressure (here, surface pressure) when the electrode is pressed.
In particular, when the predetermined temperature is set to the melting point of the resin contained in the electronic conductive material 9 or a temperature near the melting point, the adhesion between the positive electrode current collector 4 and the positive electrode active material layer 6 is further improved. The contact resistance between 4 and the positive electrode active material layer 6 can be further reduced.
Further, the electronic conductive material 9 is deformed and enters between the positive electrode active materials, and the connection between the electronic conductive materials 9 is further improved, so that more current collecting networks are formed, and the resistance of the electrode during normal operation is reduced. It can be further lowered.
Here, an example in which the dried positive electrode active material paste is pressed at a predetermined temperature and at a predetermined surface pressure has been described. However, after the dried positive electrode active material paste is pressed at a predetermined surface pressure, the positive electrode active material is pressed. The positive electrode 1 may be obtained by heating the paste at a predetermined temperature (desirably, a melting point or a temperature near the melting point).
Next, the manufacturing method of the negative electrode 2 of the battery of the present invention will be described.
(Method for producing negative electrode)
A negative electrode active material paste prepared by dispersing mesophase carbon microbeads (hereinafter abbreviated as MCMB) and PVDF in NMP on a current collector substrate (for example, a metal film having a predetermined thickness) to be a negative electrode current collector After being applied to and dried, the negative electrode 2 formed with the negative electrode active material layer 7 can be obtained by pressing at a predetermined temperature and a predetermined pressure.
Next, the manufacturing method of the battery of this invention is demonstrated.
(Battery manufacturing method)
A separator (for example, a porous polypropylene sheet) was sandwiched between the positive electrode and the negative electrode obtained by the above-described method, and both electrodes were bonded together, and then an electrolyte solution was injected to obtain a pair of batteries having a positive electrode and a negative electrode. .
The battery obtained by the above method has a characteristic that the resistance of the positive electrode increases as the temperature rises. Therefore, even if the short circuit accident occurs outside or inside the battery and the battery temperature rises, the short circuit occurs. Since the increase in current is suppressed, the safety of the battery itself is improved.
Example 1.
(Production method of positive electrode)
An electronically conductive material having characteristics of a volume resistivity of 0.2 (Ω · cm) at room temperature and a volume resistivity of 20 (Ω · cm) at 135 (degrees) (for example, 60 parts by weight of carbon black and 40 of polyethylene) The pellets contained in a weight part ratio) were finely pulverized by a jet mill method to obtain fine particles of an electronic conductive material.
Next, 6 parts by weight of the fine particles and a positive electrode active material (for example, LiCoO 2 ) And 91 parts by weight of a binder (for example, PVDF) were dispersed in NMP as a dispersion medium to obtain a positive electrode active material paste.
Next, the above-described positive electrode active material paste was applied onto a metal film (here, aluminum foil) having a thickness of 20 (μm) to be the positive electrode current collector 4 by a doctor blade method.
Furthermore, after drying at 80 (degrees), it is at a predetermined temperature (for example, room temperature) and a predetermined surface pressure (for example, 2 (ton / cm). 2 )) To obtain a positive electrode 1 in which a positive electrode active material layer 6 having a thickness of about 100 (μm) was formed on the positive electrode current collector 4.
(Method for producing negative electrode)
A negative electrode active material paste prepared by dispersing 90 parts by weight of mesophase carbon microbeads (hereinafter abbreviated as MCMB) and 10 parts by weight of PVDF in NMP, on a negative electrode current collector made of copper foil having a thickness of 20 (μm), After applying by the doctor blade method and drying at 80 (degrees), at room temperature, 2.0 (ton / cm 2 ) Pressing with pressure gave negative electrode 2 in which negative electrode active material layer 7 was formed on negative electrode current collector 5.
(Evaluation of electrodes and batteries)
In order to evaluate the electrode of the present invention and a battery using the electrode, the following method was used.
(Measurement of electrode resistance)
Aluminum foil was fused on both sides of the electrode, the positive voltage terminal and current terminal were connected to one side of one aluminum foil, and the negative side was connected to the other aluminum foil. A heater is in contact with the terminal, and the resistance value (here, the volume specific resistance (herein, the volume resistivity)) is measured by measuring the voltage drop of the element through which a constant current is passed while heating the electrode at a heating rate of 5 (degree / min). Ω · cm)).
(Capacity test)
Both the positive electrode 1 and the negative electrode 2 obtained by the above-described method were cut into a size of 14 (mm) × 14 (mm).
Next, a porous polypropylene sheet (Hoechst's trade name Celgard # 2400) was used as the separator 3, and this was sandwiched between the positive electrode 1 and the negative electrode 2 to form a unit cell.
The positive electrode current collector 4 and the negative electrode current collector 5 of the unit cell are attached by spot welding, respectively, are put in a bag made of an aluminum laminate sheet, and a mixed solvent of ethylene carbonate and diethyl carbonate (molar ratio is 1). 1) to 1.0 (mol / dm) of lithium hexafluorophosphate Three After the electrolyte solution dissolved at a concentration of) was poured, it was sealed by heat sealing to obtain a battery.
The battery was charged and discharged at room temperature, and the discharge capacity at 2C (C: time rate) was measured.
(Nail penetration test)
Both the positive electrode 1 and the negative electrode 2 obtained by the above-described method were cut into 50 (mm) × 50 (mm).
Next, a porous polypropylene sheet (Hoechst's trade name Celgard # 2400) was used as the separator 3, and this was sandwiched between the positive electrode 1 and the negative electrode 2 to form a unit cell.
10 pairs of the unit cells are stacked, and the current collecting tabs connected to the respective ends of the positive electrode current collector 4 and the negative electrode current collector 5 are spot-welded between the positive electrodes and the negative electrodes, thereby electrically connecting the batteries in parallel. To form an assembled battery.
This is put in a bag made of an aluminum laminate sheet, and lithium hexafluorophosphate is added to 1.0 (mol / dm) in a mixed solvent of ethylene carbonate and diethyl carbonate (1: 1 in molar ratio). Three After the electrolyte solution dissolved at a concentration of) was poured, it was sealed by heat sealing to obtain a battery.
This battery was charged at room temperature until it reached 4.2 (V) at 800 (mA).
After the completion of charging, an iron nail having a diameter of 2.5 (mm) was inserted into the center of the battery, and the battery temperature was measured.
FIG. 2 is a table showing the characteristics of an electrode and a battery using this electrode. Specifically, the volume specific resistance of the electrode of Example 1 (here positive electrode) and the electrode of Comparative Example 1 (here positive electrode); It is the table | surface which showed the change rate of the volume resistivity, the battery using the electrode of Example 1, and the discharge capacity of the battery using the electrode of the comparative example 1.
In the figure, the positive electrode in Comparative Example 1 was produced by using artificial graphite KS-6 (manufactured by Lonza) as an electronic conductive material in the positive electrode production method of Example 1.
The negative electrode in Comparative Example 1 was manufactured by the negative electrode manufacturing method shown in Example 1.
In the figure, the rate of resistance change is a value obtained by dividing the volume resistivity after the PTC function is expressed by the volume resistivity before the PTC function is developed.
As shown in the figure, it can be seen that, in Comparative Example 1, since the electronic conductive material does not contain a resin, the resistance change rate is smaller than that in Example 1.
It can also be seen that the discharge capacity is comparable between Comparative Example 1 and Example 1.
In Example 1, since the resin is contained in the electrode, in particular, the electronic conductive material 9 of the positive electrode active material layer 6 of the positive electrode 1, the resistance after the PTC function is developed is increased by 50 times the resistance before the development. I understand what you are doing.
Therefore, when a battery is configured using this electrode, the PTC function is manifested when the internal temperature of the battery becomes higher than a predetermined temperature, so that an increase in short-circuit current is suppressed, and the safety and reliability of the battery are further increased. improves.
In the first embodiment, the case where the resistance change rate is 50 has been described as an example. However, the present invention is not limited to this, and if the resistance change rate is about 1.5 to 10,000, the above-described effect can be obtained.
FIG. 3 is a diagram showing the characteristics of a battery using electrodes. Specifically, when a nail penetration test was performed on a battery using the electrode of Example 1 and a battery using the electrode of Comparative Example 1. It is a graph which shows the relationship between the temperature of a battery, and time passage.
In the battery using the electrode of Example 1, the PTC function works when the temperature rises to around a predetermined temperature. Therefore, the temperature starts to fall within 5 minutes after the temperature rises to around 150 (degrees). However, the battery using the electrode of Comparative Example 1 continues to rise in temperature with time.
When Example 1 and Comparative Example 1 are compared, in Example 1, resin is mixed in the electrode, in particular, the electronic conductive material 9 of the positive electrode active material layer 6 of the positive electrode 1, and thus a battery is configured using this electrode. Then, when the internal temperature of the battery becomes higher than a predetermined temperature, the function of the PTC appears, and the increase in the short circuit current is suppressed before the battery temperature exceeds 160 (degrees). Therefore, the safety and reliability of the battery Is further improved.
FIG. 4 is a diagram showing the characteristics of a battery using an electrode. Specifically, when a nail penetration test was performed on a battery using the electrode of Example 1 and a battery using the electrode of Comparative Example 2. It is a figure which shows the relationship between the temperature of a battery, and time passage.
In the figure, the positive electrode of Comparative Example 2 was manufactured using a pellet containing carbon black and polypropylene resin (melting point: 168 (degrees)) as the electronic conductive material 9 in the positive electrode manufacturing method of Example 1. Is.
The negative electrode in Comparative Example 2 was manufactured by the negative electrode manufacturing method shown in Example 1.
As shown in the figure, in Comparative Example 2, since a polypropylene resin having a melting point of 168 (degrees) was used as the resin contained in the electronic conductive material 9, when a battery was configured using an electrode containing this resin, PTC It is considered that the temperature at which this function is manifested exceeds 160 (degrees).
On the other hand, in Example 1, since polyethylene having a melting point lower than 160 (degrees) is used as the resin, the increase in short-circuit current is suppressed before the battery temperature exceeds 160 (degrees). Reliability is further improved.
In the battery using the electrode of Example 1, the PTC function works when the temperature rises, and after the temperature rises to around 150 (degrees), the temperature starts to drop, but the battery using the electrode of Comparative Example 2 is PTC. The temperature at which this function is manifested is high, and the temperature continues to rise even when the temperature reaches 200 (degrees) or more.
This is because the melting point of the resin (here, polypropylene resin) included in the electronic conductive material is higher than 160 (degrees).
Therefore, if the resin contained in the electronic conductive material 9 is selected from those having a melting point in the range of 90 (degrees) to 160 (degrees), the battery performance is not deteriorated and the function of PTC is exhibited. The temperature can be lower than 160 (degrees).
FIG. 5 is a table showing the characteristics of an electrode and a battery using this electrode. Specifically, the volume specific resistance of the electrode, the resistance change rate when the temperature rises, and the discharge at 2C (C: time rate) of the battery It is a table | surface figure which shows the value of a capacity | capacitance, and the temperature of the battery 10 minutes after a nail penetration test start.
In the figure, Comparative Example 3 is a method for manufacturing a positive electrode of Example 1, and an electrode (here, positive electrode) is used as the electronic conductive material 9 using pellets containing 38 parts by weight of carbon black and 62 parts by weight of polyethylene. 1) is manufactured, and a battery is manufactured using this electrode.
In Comparative Example 3, the manufacturing method of the negative electrode is the same as that in Example 1.
Further, Comparative Example 4 is a method for producing a positive electrode of Example 1, in which an electrode containing 71 parts by weight of carbon black and 29 parts by weight of polyethylene as an electronic conductive material (here, positive electrode 1) is used. And a battery using this electrode.
In Comparative Example 4, the manufacturing method of the negative electrode is the same as that in Example 1.
As shown in the figure, the resistance change rate of Comparative Example 3 was larger than that of Example 1, but the resistance value of the electrode was high and the discharge capacity was low.
Moreover, although the discharge capacity of Comparative Example 4 is higher than that of Example 1, the temperature after 10 minutes is very high when the nail penetration test is performed because the function of PTC is insufficient because the ratio of carbon black is too large. It became high.
Therefore, by changing the ratio of the conductive filler contained in the electronic conductive material 9, the resistance change rate of the electrode and the discharge capacity of the battery can be set to appropriate values.
In particular, by setting the ratio of the conductive filler contained in the electrode (here, positive electrode 1) to 40 parts by weight to 70 parts by weight, the resistance of the electrode at normal time (before the function of PTC is manifested) is lowered, The rate of change in resistance of the electrode can be increased, and the discharge capacity when a battery is configured using this electrode can be increased.
Furthermore, by setting the proportion of the conductive filler contained in the electronic conductive material to 50 to 68 parts by weight, the electrode characteristics and battery characteristics shown in FIG. 5 can be made more desirable. .
FIG. 6 is a diagram showing the characteristics of an electrode and a battery using this electrode. Specifically, the relationship between the ratio of the electron conductive material and the volume resistivity of the electrode, the ratio of the electron conductive material and the discharge capacity In detail, the relationship between the ratio of the electronic conductive material to the total solid content of 100 parts by weight of the positive electrode active material layer of the battery and the volume resistivity of the electrode ((a) in the figure) and the battery It is a figure which shows the relationship ((b) in a figure) of the ratio of the electronic conductive material with respect to 100 weight part of total solids of a positive electrode active material layer, and discharge capacity.
As shown in the figure, when the ratio of the electronic conductive material 9 is 0.5 parts by weight or less, the resistance value of the electrode itself in a normal state is too high and the discharge capacity is low, which causes a problem in terms of battery performance.
On the other hand, when the amount is 15 parts by weight or more, the discharge capacity is lowered by reducing the amount of the active material.
Therefore, by setting the ratio of the electronic conductive material 9 contained in the electrode to 0.5 to 15 parts by weight, the resistance of the electrode during normal operation is lowered, and the discharge capacity of the battery using this electrode is increased. can do.
More preferably, the ratio of the electroconductive material to 100 parts by weight of the total solid content of the electrode (here positive electrode) is 0.7 to 12 parts by weight, more preferably 1 to 10 parts by weight. The above characteristics can be made more desirable.
FIG. 7 is a diagram showing the relationship between the particle diameter of the electron conductive material and the resistance of the electrode ((a) in the figure) and the relationship between the particle diameter of the electron conductive material and the discharge capacity ((b) in the figure). is there.
When the particle diameter of the electron conductive material 9 is 0.05 (μm) or less, the filling rate of the electron conductive material 9 decreases, and the volume of the electron conductive material 9 per unit volume of the positive electrode active material layer 6 increases. That is, the positive electrode active material weight per unit volume of the positive electrode active material layer 6 is reduced.
For this reason, when the particle diameter of the electronic conductive material 9 is 0.05 (μm) or less, the discharge capacity is lowered.
When the particle diameter of the electronic conductive material 9 is 100 (μm) or more, the resistance value of the electrode itself is high and the discharge capacity is low.
Therefore, when the average particle diameter of the electronic conductive material 9 is 0.05 (μm) to 100 (μm), the resistance of the electrode during normal operation can be lowered and the discharge capacity can be increased.
Further, if the average particle size of the electronic conductive material 9 is 0.1 (μm) to 50 (μm), more preferably 0.5 (μm) to 20 (μm), the volume of the electronic conductive material 9 is increased. The rate, the volume resistivity of the electrode itself, and the discharge capacity can be made more desirable.
FIG. 8 is a table showing the average particle diameter of the electronic conductive material, the resistance of the electrode, and the discharge capacity of the battery.
In the figure, Comparative Example 5 is an electrode (here, positive electrode 1) manufactured using a material obtained by pulverizing an electronic conductive material by a ball mill method.
In Comparative Example 5, the manufacturing method of the negative electrode is the same as that in Example 1.
In Comparative Example 5, since the electron conductive material is pulverized by the ball mill method, the average particle diameter of the particles of the obtained electron conductive material 9 is increased, and as a result, the volume specific resistance of the electrode is high and the discharge capacity is small. I understand.
Therefore, it can be seen that it is desirable to pulverize the electroconductive material by the jet mill method in order to reduce the resistance of the electrode during normal operation and to increase the discharge capacity of the battery.
Example 2
Example 2 is the same as in Example 1, except that the positive electrode active material paste was applied on an aluminum foil, dried at 80 (degrees), and then 0.5 (ton / cm at 135 (degrees). 2 ) For 30 minutes to produce an electrode (here, positive electrode 1).
In Example 2, the manufacturing method of the negative electrode is the same as that of Example 1.
FIG. 9 is a table showing the characteristics of the electrode of Example 2 and a battery using this electrode.
As shown in the drawing, in Example 2, when the dried positive electrode active material paste is pressed, the positive electrode current collector 4 and the positive electrode active material layer are pressed at a temperature near the melting point of the resin contained in the electronic conductive material 9. 6 and the contact resistance between the positive electrode current collector 4 and the positive electrode active material layer 6 can be reduced.
Furthermore, since the electron conductive material 9 is deformed and spreads between the positive electrode active materials 8, the connection between the electron conductive materials 9 is improved, so that more current collecting networks are formed, and the positive electrode active material layer in the normal state. The resistance of 6 can be lowered.
Thereby, the resistance of the electrode (here, positive electrode 1) during normal operation can be further reduced.
This means that the resistance value of the obtained electrode can be adjusted by adjusting the temperature or pressure (here, surface pressure) when pressing the dried positive electrode active material paste.
If the temperature at which the dried positive electrode active material paste is pressed is the melting point of the resin contained in the electronic conductive material or a temperature near the melting point, even if the pressure is reduced to some extent, the pressing is performed at a temperature near the melting point of the resin. Therefore, the value of the volume resistivity at the normal time of the obtained electrode can be reduced.
Example 3
(Production method of positive electrode)
An electronically conductive material (for example, carbon black and polyethylene having a specific volume resistivity of 0.2 (Ω · cm) at room temperature and a specific volume of 500 (Ω · cm) at an operating temperature of 135 (degrees) The pellets having a proportion) were pulverized by a jet mill method to obtain fine particles of an electronically conductive material having an average particle size of 9.0 (μm).
4.5 parts by weight of fine particles of the electronic conductive material, 1.5 parts by weight of artificial graphite KS-6 (manufactured by Lonza) as a conductive assistant, 91 parts by weight of an active material (for example, LiCoO 2), and a binder (for example, PVDF) ) Was dispersed in NMP as a dispersion medium to obtain a positive electrode active material paste adjusted.
Next, the above-described positive electrode active material paste was applied onto a metal film (here, aluminum foil) having a thickness of 20 (μm) to be the positive electrode current collector 4 by a doctor blade method. Furthermore, after drying at 80 (degrees), at a predetermined temperature (for example, room temperature) and a predetermined surface pressure (for example, 2 (ton / cm 2 )) To obtain a positive electrode 1 in which a positive electrode active material layer 6 having a thickness of about 100 (μm) was formed on the positive electrode current collector 4. Moreover, the manufacturing method of the negative electrode of Example 3 is the same as that of Example 1.
FIG. 10 is a diagram showing the characteristics of an electrode and a battery using this electrode. Specifically, the volume specific resistance of the electrode of Example 1, the discharge capacity of the battery using the electrode of Example 1, It is a table | surface which shows the temperature of the battery 10 minutes after a test start, the volume specific resistance of the electrode of Example 3, the discharge capacity of the battery using the electrode of Example 3, and the temperature of the battery 10 minutes after the start of the nail insertion test. .
Compared to Example 1, the electrode of Example 3 had a discharge capacity substantially the same as that of Example 1.
In other words, even when an electron conductive material with a high volume resistivity is used, by adding a conductive auxiliary agent, the volume resistivity of the electrode during normal operation is lowered and the discharge capacity of a battery using this electrode is increased. Can be.
Here, the conductive assistant is graphite (here artificial graphite KS-6 (manufactured by Lonza)), but it is not necessary to be limited to this, and the electronic conductivity of the electrode such as carbon black such as acetylene black and lamp black. What is the conductive aid if it is a substance whose resistance hardly changes as the temperature rises (or a substance that enhances electronic conductivity and does not have a PTC function)? Also good.
Example 4
The positive electrode of the battery of Example 4 is an electron conductive material obtained by further pulverizing fine particles of an electronic conductive material obtained by pulverizing an electronic conductive material by a composite pulverization method in the method for producing a positive electrode of Example 1 by a jet mill method. An electrode (here, positive electrode 1) is formed using fine particles.
The manufacturing method of the negative electrode of Example 4 is the same as that of Example 1.
FIG. 11 is a table showing the average particle diameter of the electron conductive material used for the electrode of Example 4 (here, positive electrode 1).
According to the figure, it can be seen that the average particle diameter of Example 4 is smaller than that of Example 1.
This is because, after the particle size of the electronic conductive material is reduced in advance by the composite pulverization method, the electron conductive material is further pulverized by the jet mill method. Both can be reduced, and the time required for pulverizing the electronic conductive material can be shortened.
Therefore, when an electrode is manufactured using this electronic conductive material, an electrode having high flexibility and easy processing can be obtained.
Further, in Example 4, the positive electrode has been described as an example, but the same effect can be obtained even when applied to the negative electrode.
Embodiment 5 FIG.
The positive electrode of Example 5 was obtained by pulverizing the electronic conductive material in Example 4 while cooling it by a composite pulverization method, and using the resulting fine particles of the electronic conductive material to form an electrode (positive electrode 1 in this case). It is a feature.
The manufacturing method of the negative electrode of Example 5 is the same as that of Example 1.
FIG. 12 is a table showing the particle diameter of the electronic conductive material before pulverization by the composite pulverization method and the particle diameter of the electronic conductive material after pulverization by the composite pulverization method.
According to the figure, when the electronic conductive material is pulverized by the composite pulverization method, the particle diameter can be made smaller by pulverizing the electronic conductive material while cooling.
Therefore, if the electron conductive material is pulverized while cooling, the particle size and variation in particle size of the obtained electron conductive material can be further reduced, so that an electrode having higher flexibility and easier processing can be obtained. .
Example 6
The electrode of Example 6 is characterized by having at least two kinds of electronic conductive materials.
Here, a case where the positive electrode active material layer 6 of the positive electrode 1 has two types of electronic conductive materials will be described as an example.
The method for producing the positive electrode and the method for producing the negative electrode of Example 6 will be described below.
(Production method of positive electrode)
Fine particles of the first electronic conductive material were obtained by finely pulverizing the first electronic conductive material (for example, pellets containing 70 parts by weight of carbon black and 30 parts by weight of polyethylene) by a jet mill method.
Also, fine particles of the second electronic conductive material are obtained by finely pulverizing the second electronic conductive material (for example, pellets containing 90 parts by weight of tungsten carbide and 10 parts by weight of polyethylene) by a jet mill method. It was.
Next, 4.2 parts by weight of the fine particles of the first electronic conductive material, 1.8 parts by weight of the fine particles of the second electronic conductive material, and a positive electrode active material (for example, LiCoO 2 ) And 3 parts by weight of a binder (for example, PVDF) were dispersed in NMP as a dispersion medium to obtain a positive electrode active material paste.
Next, the above-described positive electrode active material paste was applied onto a metal film (here, aluminum foil) having a thickness of 20 (μm) to be the positive electrode current collector 4 by a doctor blade method. Furthermore, after drying at 80 (degrees), at a predetermined temperature (for example, room temperature) and a predetermined surface pressure (for example, 2 (ton / cm 2 )) To obtain a positive electrode 1 in which a positive electrode active material layer 6 having a thickness of about 100 (μm) was formed on the positive electrode current collector 4.
The negative electrode manufacturing method of Example 6 is the same as that of Example 1.
In order to confirm the performance of the electrode of Example 6 and the battery using this electrode, the following tests were conducted.
(Short-circuit test)
The positive electrode 1 and the negative electrode 2 obtained by the above-described method were each cut into a size of 38 (mm) × 65 (mm).
A polypropylene sheet (Hoechst Celgard # 2400) is used as the separator 3, and the separator 3 is placed between the positive electrode and the negative electrode. A current collecting tab is attached to each end of the current collector 4 and the negative electrode current collector 5 by ultrasonic welding, and this is put into a bag made of an aluminum laminate sheet, and a mixed solvent of ethylene carbonate and diethyl carbonate (in molar ratio). 1: 1) to 1.0 (mol / dm) of lithium hexafluorophosphate Three After the electrolyte solution dissolved at a concentration of) was poured, it was sealed by heat sealing to obtain a battery.
This battery was charged at room temperature until it reached 4.2 (V) at 80 (mA). After completion of charging, the battery was heated in the oven, and the current value when short-circuited at 145 (degrees) was measured.
FIG. 13 is a diagram showing the characteristics of an electrode and a battery using this electrode. Specifically, the table shows the volume resistivity of the electrode, the flexibility of the electrode, and the short-circuit current value of the battery using this electrode. FIG.
In the figure, ◯ indicates that the electrode has a considerably good flexibility, and Δ indicates that it is moderately good.
From the figure, it can be seen that in Example 6, the volume resistivity is lower, the flexibility is higher, and the short-circuit current is lower than in Comparative Example 1.
Accordingly, if the electrode (here, the positive electrode active material layer 6 of the positive electrode 1) contains at least two kinds of electronic conductive materials, resistance at a temperature lower than a predetermined temperature is low, flexibility is high, and processing is performed. Can be obtained.
Furthermore, when a battery is configured using this electrode, a short-circuit accident occurs outside or inside the battery, and even if the battery temperature rises, the short-circuit current flowing inside the battery decreases, so a battery with high safety is obtained. be able to.
In the sixth embodiment, the electrode includes two types of electron conductive materials. However, the present invention is not limited to this.
In short, the above-described effects can be obtained by using a plurality of types of electronic conductive materials included in the electrodes.
Example 7
The electronically conductive material contained in the electrode of Example 7 is characterized by having at least two kinds of conductive fillers.
Here, an example in which the electronic conductive material 9 of the positive electrode active material layer 6 of the positive electrode 1 has two types of conductive fillers will be described.
The method for producing the positive electrode and the method for producing the negative electrode of Example 7 will be described below.
(Production method of positive electrode)
As the conductive filler, a material containing carbon black and tungsten carbide (mixing ratio is, for example, 75 parts by weight: 25 parts by weight), and the pellet containing the conductive filler and the resin (here, polyethylene) is electronically conductive. Material.
The electronic conductive material was pulverized by, for example, a jet mill method to obtain fine particles of the electronic conductive material.
6 parts by weight of fine particles of the electron conductive material, positive electrode active material (for example, LiCoO 2 ) And 91 parts by weight of a binder (for example, PVDF) and 3 parts by weight of a binder (for example, NMP) were dispersed in a dispersion medium (for example, NMP) to prepare a positive electrode active material paste.
The subsequent manufacturing method of the positive electrode is the same as in Example 1.
Moreover, the manufacturing method of a negative electrode is the same as Example 1.
A test was conducted to confirm the performance of the electrode of Example 7 and the battery using this electrode.
FIG. 14 is a table showing the characteristics of an electrode and a battery using this electrode, and specifically shows the volume resistivity of the electrode, the flexibility of the electrode, and the short-circuit current value of the battery using this electrode. FIG.
In the figure, ◯ indicates that the electrode has a considerably good flexibility, and Δ indicates that it is moderately good.
From the figure, the volume specific resistance of the electrode in the normal state is lower in Example 7 than in Comparative Example 1. In addition, the flexibility of the electrode is increased. Moreover, it turns out that the value of the short circuit current of the battery using the electrode of Example 7 also becomes low.
Therefore, if the electronic conductive material 9 includes at least two kinds of conductive fillers, an electrode having low resistance at a temperature lower than a predetermined temperature, high flexibility, and easy processing can be obtained. it can.
Furthermore, when a battery is configured using this electrode, a short-circuit accident occurs outside or inside the battery, and even if the battery temperature rises, the short-circuit current flowing inside the battery decreases, so a battery with high safety is obtained. be able to.
In the seventh embodiment, the electronic conductive material 9 is described as an example including two kinds of conductive fillers, but is not limited thereto.
In short, if the electronic conductive filler 9 has a plurality of types of conductive fillers, the above-described effects can be obtained.
Example 8 FIG.
The electrode of Example 8 is characterized by having different types of resins.
Here, an example in which the electron conductive material 9 of the positive electrode active material layer 6 of the positive electrode 1 has two types of resins will be described.
The method for producing the positive electrode and the method for producing the negative electrode in Example 8 will be described below.
(Production method of positive electrode)
Example 1 is the same as Example 1 except that the resin is a mixture of polyethylene and polypropylene in a predetermined ratio (for example, the mixing ratio is 75 parts by weight: 25 parts by weight).
Moreover, the manufacturing method of the negative electrode of Example 8 is the same as that of Example 1.
A test was conducted to confirm the performance of the electrode of Example 8 and the battery using this electrode.
FIG. 15 is a diagram showing the characteristics of an electrode and a battery using this electrode. Specifically, the table shows the volume resistivity of the electrode, the flexibility of the electrode, and the short-circuit current value of the battery using this electrode. FIG.
From the figure, the volume resistivity of the electrode in the normal state is lower in Example 8 than in Comparative Example 1. Moreover, it turns out that the short circuit current value of the battery using the electrode of Example 8 also becomes low.
Therefore, if the electronic conductive material 9 contains at least two kinds of resins, an electrode having a low resistance at a temperature lower than a predetermined temperature can be obtained.
Furthermore, when a battery is configured using this electrode, a short-circuit accident occurs outside or inside the battery, and even if the battery temperature rises, the short-circuit current flowing inside the battery decreases, so a battery with high safety is obtained. be able to.
In the eighth embodiment, the electronic conductive material 9 is described as an example having two kinds of resins, but is not limited thereto.
Even when the electronic conductive filler 9 has a plurality of types of resins, the above-described effects can be obtained.
If the melting point of at least one of these resins is between 90 (degrees) and 160 (degrees), the function of PTC is manifested in this temperature range.
Accordingly, a resin other than this resin whose melting point is not within the above range may be used.
Moreover, it becomes possible to arbitrarily adjust the temperature at which the PTC function is manifested by changing the ratio of the plurality of types of resins.
Example 9
The electrode of Example 9 is characterized in that an electrode is formed using a manganese-based oxide as an active material.
Here, as the positive electrode active material 8 used for the positive electrode 1, LiMn 2 O Four The positive electrode 1 was manufactured using the battery, and the battery was configured using the positive electrode 1.
The positive electrode manufacturing method of Example 9 is the same as the positive electrode manufacturing method of Example 1, except that LiMn is used as the positive electrode active material. 2 O Four Example 1 is the same as Example 1 except that is used.
Moreover, the manufacturing method of the negative electrode of Example 9 is the same as that of Example 1.
A short circuit test was performed to confirm the performance of the electrode and battery of Example 9.
FIG. 16 is a table showing the short-circuit current values of the battery using the electrode of Example 1 and the battery using the electrode of Example 9.
As shown in the figure, as the active material (here, positive electrode active material 8), LiMn 2 O Four It can be seen that the value of the short-circuit current is about the same as that of Example 1 even when using.
Therefore, when the battery is configured using the electrode of Example 9, a short circuit accident occurs outside or inside the battery, and even if the temperature of the battery rises, the short circuit current flowing inside the battery decreases. A high battery can be obtained.
Example 10
The electrode of Example 10 is characterized in that an electrode is formed using an iron-based oxide as an active material.
Here, as a positive electrode active material used for the positive electrode, Fe 2 (SO Four ) Three A positive electrode is formed using the positive electrode, and an electrode is formed using the positive electrode.
The positive electrode manufacturing method of Example 10 is the same as the positive electrode manufacturing method of Example 1, except that Fe 2 (SO Four ) Three Example 1 is the same as Example 1 except that is used.
Moreover, the manufacturing method of the negative electrode of Example 10 is the same as that of Example 1.
A short circuit test was conducted to confirm the performance of the electrode of Example 10 and the battery using this electrode.
FIG. 17 is a table showing the short-circuit current values of the battery using the electrode of Example 1 and the battery using the electrode of Example 10.
As shown in the figure, as the active material (here, positive electrode active material 8), Fe 2 (SO Four ) Three It can be seen that the value of the short-circuit current is about the same as that of Example 1 even when using.
Therefore, when the battery is configured using the electrode of Example 10, a short circuit accident occurs outside or inside the battery, and even if the temperature of the battery rises, the short circuit current flowing inside the battery decreases, and safety is improved. A high battery can be obtained.
Example 11
FIG. 18 is a view showing an example in which the above-described electrode and battery are applied to a lithium ion secondary battery, and more specifically, a cross-sectional view showing the structure of a cylindrical lithium ion secondary battery.
In the figure, reference numeral 200 denotes an outer can made of stainless steel that also serves as a negative electrode terminal, 100 denotes a battery body housed in the outer can 200, and the battery body 100 winds the positive electrode 1, the separator 3, and the negative electrode 2 in a spiral shape. It has a structure.
The positive electrode 1 of the battery body 100 has the positive electrode configuration described above.
By doing so, the current increases due to a short circuit outside or inside the battery, and the resistance of the positive electrode 1 (particularly the positive electrode active material layer) itself increases when the temperature of the battery or the electrode rises to a certain extent. The current flowing inside the battery is reduced.
Therefore, when a battery is configured using this electrode, the safety of the battery is dramatically improved, and the safety of the battery is maintained even in the case of an abnormality such as a short circuit, reverse charge or overcharge under severe conditions. There is an effect.
Here, the positive electrode 1 has been described as an example in which the resistance increases as the temperature rises. However, the negative electrode 2 (particularly, the negative electrode active material layer) includes an electronic conductive material containing a resin and a conductive filler. If so, the resistance of the negative electrode 2 increases as the temperature rises, so that the same effect as described above can be obtained.
The electrodes and batteries shown in the above-described embodiments are not only organic electrolyte type, solid electrolyte type and gel electrolyte type lithium ion secondary batteries, but also primary batteries such as lithium / manganese dioxide batteries, and other secondary batteries. Can be used.
Furthermore, it is also effective for aqueous solution type primary batteries and secondary batteries. Furthermore, it can be used for primary and secondary batteries such as a stacked type, a wound type, and a button type regardless of the battery shape.
Industrial applicability
The electrodes and batteries according to the present invention can be used not only in organic electrolyte type, solid electrolyte type and gel electrolyte type lithium ion secondary batteries, but also in primary batteries such as lithium / manganese dioxide batteries, and other secondary batteries. is there.
Furthermore, it is also effective for aqueous solution type primary batteries and secondary batteries. Furthermore, it can be used for primary and secondary batteries such as a stacked type, a wound type, and a button type regardless of the battery shape.

Claims (15)

活物質と、
この活物質に接触する電子導電性材料とを有する電極であって、
上記電子導電性材料は、導電性充填材と樹脂とを含有し、温度が上昇するとともに、その抵抗が増加するように構成し、上記電子導電性材料の粒径は０．０５（μｍ）〜１００（μｍ）としたことを特徴とする電極。Active material,
An electrode having an electronically conductive material in contact with the active material,
The electronic conductive material includes a conductive filler and a resin, and is configured to increase its resistance with increasing temperature. The particle diameter of the electronic conductive material is 0.05 (μm) to An electrode characterized by being 100 (μm) . 電子導電性材料の樹脂は９０（度）〜１６０（度）の範囲内で融点を有するものを用いたことを特徴とする特許請求の範囲第１項に記載の電極。2. The electrode according to claim 1, wherein the resin of the electronically conductive material has a melting point within a range of 90 (degrees) to 160 (degrees). 電子導電性材料を活物質層の全固形分１００重量部に対し０．５〜１５重量部含有した特許請求の範囲第１項に記載の電極。The electrode according to claim 1, wherein the electroconductive material is contained in an amount of 0.5 to 15 parts by weight with respect to 100 parts by weight of the total solid content of the active material layer . 電子導電性材料の導電性充填材の割合が４０重量部〜７０重量部としたことを特徴とする特許請求の範囲第１項に記載の電極。The electrode according to claim 1, wherein the ratio of the conductive filler of the electronic conductive material is 40 to 70 parts by weight. 導電性充填材はカーボン材料または導電性非酸化物としたことを特徴とする特許請求の範囲第１項に記載の電極。The electrode according to claim 1, wherein the conductive filler is a carbon material or a conductive non-oxide. 電極は電子導電性を高めるものであって、温度の上昇に伴いその抵抗がほとんど変化しない導電助剤を含むことを特徴とする特許請求の範囲第１項に記載の電極。The electrode according to claim 1, wherein the electrode includes a conductive additive that enhances electronic conductivity and whose resistance hardly changes with an increase in temperature. 少なくとも種類の異なる２つの電子導電性材料を含有することを特徴とする特許請求の範囲第１項に記載の電極。The electrode according to claim 1, comprising at least two different types of electronic conductive materials. 電子導電性材料は少なくとも種類の異なる２つの導電性充填材を含有することを特徴とする特許請求の範囲第１項に記載の電極。The electrode according to claim 1, wherein the electronically conductive material contains at least two kinds of different conductive fillers. 電子導電性材料は少なくとも種類の異なる２つの樹脂を含有することを特徴とする特許請求の範囲第１項に記載の電極。The electrode according to claim 1, wherein the electronically conductive material contains at least two kinds of different resins. 正極と、
負極と、
上記正極および上記負極の間にセパレータを備え、
上記正極または上記負極に特許請求の範囲第１項から第９項のいずれかに記載の電極を用いたことを特徴とする電池。A positive electrode;
A negative electrode,
A separator is provided between the positive electrode and the negative electrode,
A battery comprising the electrode according to any one of claims 1 to 9 as the positive electrode or the negative electrode. 電極の製造方法であって、
（ａ）導電性充填材と樹脂とを含有する電子導電性材料を粉砕する工程
（ｂ）上記粉砕した電子導電性材料を分散させることにより活物質ペーストを製造する工程
（ｃ）上記活物質ペーストを乾燥させたものを所定の温度、所定の圧力でプレスする工程
なる工程を有することを特徴とする電極の製造方法。An electrode manufacturing method comprising:
(A) A step of pulverizing an electronic conductive material containing a conductive filler and a resin (b) A step of manufacturing an active material paste by dispersing the pulverized electronic conductive material (c) The active material paste A method for producing an electrode, comprising: a step of pressing a dried product at a predetermined temperature and a predetermined pressure. 所定の温度を樹脂の融点または融点付近の温度としたことを特徴とする特許請求の範囲第１１項に記載の電極の製造方法。12. The method of manufacturing an electrode according to claim 11, wherein the predetermined temperature is a melting point of the resin or a temperature near the melting point. 導電性充填材と樹脂とを含有する電子導電性材料を粉砕する工程は、超音速流にのせた上記電子導電性材料を壁面にあてるかまたは上記電子導電性材料を互いに衝突させることにより、上記電子導電性材料を粉砕することを特徴とする特許請求の範囲第１１項に記載の電極の製造方法。The step of pulverizing the electronic conductive material containing the conductive filler and the resin is performed by applying the electronic conductive material placed on a supersonic flow to a wall surface or colliding the electronic conductive material with each other. The method for manufacturing an electrode according to claim 11 , wherein the electroconductive material is pulverized. 導電性充填材と樹脂とを含有する電子導電性材料を粉砕する工程は、上記電子導電性材料に剪断力、磨砕力および衝撃力を複合的に与えることにより上記電子導電性材料を粉砕することを特徴とする特許請求の範囲第１１項に記載の電極の製造方法。In the step of pulverizing the electronic conductive material containing the conductive filler and the resin, the electronic conductive material is pulverized by combining the electronic conductive material with a shearing force, a grinding force and an impact force. The method for manufacturing an electrode according to claim 11 , wherein: 電子導電性材料を冷却しながら粉砕することを特徴とする特許請求の範囲第１４項に記載の電極の製造方法。The method for producing an electrode according to claim 14 , wherein the electron conductive material is pulverized while being cooled.
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